I get a test failure running "make check" with the latest Emacs master
(commit bd39ec062d0078c97140b8ad4ddf7c47e6f6e4ee). I've been getting
this for a while, on both Ubuntu 24.10 and Fedora 41 (both x86-64). Here
are symptoms:

$ (cd test && make lisp/emacs-lisp/lisp-mode-tests)
make[1]: Entering directory '/home/eggert/src/gnu/emacs/tmp/test'
   GEN      lisp/emacs-lisp/lisp-mode-tests.log
Running 23 tests (2025-01-31 14:20:43-0800, selector ‘(not (or (tag
:unstable) (tag :nativecomp)))’)
    passed   1/23  indent-sexp (0.000801 sec)
    passed   2/23  indent-sexp-cant-go (0.000081 sec)
    passed   3/23  indent-sexp-go (0.000103 sec)
    passed   4/23  indent-sexp-in-string (0.000070 sec)
    passed   5/23  indent-sexp-stop (0.000074 sec)
    passed   6/23  indent-sexp-stop-before-eol-comment (0.000069 sec)
    passed   7/23  indent-sexp-stop-before-eol-non-lisp (0.014561 sec)
    passed   8/23  indent-subsexp (0.000081 sec)
    passed   9/23  lisp-comment-indent-1 (0.000105 sec)
    passed  10/23  lisp-comment-indent-2 (0.000082 sec)
'(description "This is a very long string which is indented by a
considerable value, causing it to protrude from the configured
`fill-column' since lisp-fill-paragraph was refactored in version 28.")
    passed  11/23  lisp-fill-paragraph-as-displayed (0.000216 sec)
    passed  12/23  lisp-fill-paragraph-docstring-boundaries (0.000118 sec)
Test lisp-fontify-confusables backtrace:
   signal(ert-test-failed (((should (faceup-test-font-lock-buffer 'emac
   ert-fail(((should (faceup-test-font-lock-buffer 'emacs-lisp-mode fac
   (if (unwind-protect (setq value-122 (apply fn-120 args-121)) (setq f
   (let (form-description-124) (if (unwind-protect (setq value-122 (app
   (let ((value-122 'ert-form-evaluation-aborted-123)) (let (form-descr
   (let* ((fn-120 #'faceup-test-font-lock-buffer) (args-121 (condition-
   (let ((faceup (buffer-string))) (faceup-clean-buffer) (let* ((fn-120
   (progn (let ((tail '(8216 8217 8219 8220 8221 8223 12318 65282 65287
   (unwind-protect (progn (let ((tail '(8216 8217 8219 8220 8221 8223 1
   (save-current-buffer (set-buffer temp-buffer) (unwind-protect (progn
   (let ((temp-buffer (generate-new-buffer " *temp*" t))) (save-current
   #f(lambda () [t] (let ((temp-buffer (generate-new-buffer " *temp*" t
   #f(compiled-function () #<bytecode -0x6d135f9ef4d75f7>)()
   handler-bind-1(#f(compiled-function () #<bytecode -0x6d135f9ef4d75f7
   ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
   ert-run-test(#s(ert-test :name lisp-fontify-confusables :documentati
   ert-run-or-rerun-test(#s(ert--stats :selector ... :tests ... :test-m
   ert-run-tests((not (or (tag :unstable) (tag :nativecomp))) #f(compil
   ert-run-tests-batch((not (or (tag :unstable) (tag :nativecomp))))
   ert-run-tests-batch-and-exit((not (or (tag :unstable) (tag :nativeco
   eval((ert-run-tests-batch-and-exit '(not (or (tag :unstable) (tag :n
   command-line-1(("-L" ":." "-l" "ert" "--eval" "(setq treesit-extra-l
   command-line()
   normal-top-level()
Test lisp-fontify-confusables condition:
     (ert-test-failed
      ((should (faceup-test-font-lock-buffer 'emacs-lisp-mode faceup))
       :form
       (faceup-test-font-lock-buffer emacs-lisp-mode
                                    "«w:‘»foo \\‘foo\n«w:’»foo \\’foo\n«w:‛»foo \\‛foo\n«w:“»foo
\\“foo\n«w:”»foo \\”foo\n«w:‟»foo \\‟foo\n«w:〞»foo \\〞foo\n«w:＂»foo
\\＂foo\n«w:＇»foo \\＇foo\n")
       :value nil :explanation
       ((on-line 1 ("«w:‘»foo \\‘foo") ("«w:«:quote:‘»»foo \\‘foo"))
        (on-line 2 ("«w:’»foo \\’foo") ("«w:«:quote:’»»foo \\’foo"))
        (on-line 3 ("«w:‛»foo \\‛foo") ("«w:«:quote:‛»»foo \\‛foo"))
        (on-line 4 ("«w:“»foo \\“foo") ("«w:«:quote:“»»foo \\“foo"))
        (on-line 5 ("«w:”»foo \\”foo") ("«w:«:quote:”»»foo \\”foo"))
        (on-line 6 ("«w:‟»foo \\‟foo") ("«w:«:quote:‟»»foo \\‟foo"))
        (on-line 7 ("«w:〞»foo \\〞foo") ("«w:«:quote:〞»»foo \\〞foo"))
        (on-line 8 ("«w:＂»foo \\＂foo") ("«w:«:quote:＂»»foo \\＂foo"))
        (on-line 9 ("«w:＇»foo \\＇foo") ("«w:«:quote:＇»»foo \\＇foo")))))
    FAILED  13/23  lisp-fontify-confusables (0.000562 sec) at
lisp/emacs-lisp/lisp-mode-tests.el:361
Indenting region...
Indenting region...done
    passed  14/23  lisp-indent-defun (0.000928 sec)
Indenting region...
Indenting region...done
Indenting region...
Indenting region...done
Indenting region...
Indenting region...done
    passed  15/23  lisp-indent-region (0.000568 sec)
Indenting region...
Indenting region...done
    passed  16/23  lisp-indent-region-after-string-literal (0.000118 sec)
Indenting region...
Indenting region...done
    passed  17/23  lisp-indent-region-defun-with-docstring (0.000108 sec)
Indenting region...
Indenting region...done
    passed  18/23  lisp-indent-region-in-sexp (0.000119 sec)
Indenting region...
Indenting region...done
    passed  19/23  lisp-indent-region-open-paren (0.000102 sec)
Indenting region...
Indenting region...done
    passed  20/23  lisp-indent-unfinished-string (0.000049 sec)
    passed  21/23  lisp-indent-with-read-only-field (0.000048 sec)
    passed  22/23  test-font-lock-keywords (0.002377 sec)
    passed  23/23  test-lisp-current-defun-name (0.010519 sec)

Ran 23 tests, 22 results as expected, 1 unexpected (2025-01-31
14:20:43-0800, 0.082472 sec)

1 unexpected results:
    FAILED  lisp-fontify-confusables

make[1]: *** [Makefile:185: lisp/emacs-lisp/lisp-mode-tests.log] Error 1
make[1]: Leaving directory '/home/eggert/src/gnu/emacs/tmp/test'
make: *** [Makefile:251: lisp/emacs-lisp/lisp-mode-tests] Error 2