Fix font-lock-keywords slightly

* lisp/font-lock.el (font-lock-keywords): Tweak doc string
slightly (bug#35005).
1 job for master in 90 minutes and 2 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #4164
test-all

01:30:02

 
Name Stage Failure
failed
test-all Test The script exceeded the maximum execution time set for the job
  GEN      lisp/eshell/eshell-tests.log
ELC lisp/faces-tests.elc
GEN lisp/faces-tests.log
ELC lisp/ffap-tests.elc
GEN lisp/ffap-tests.log
ELC lisp/filenotify-tests.elc
GEN lisp/filenotify-tests.log
Pulling docker image gitlab/gitlab-runner-helper:x86_64-d0b76032 ...
ERROR: Job failed: execution took longer than 1h30m0s seconds