Fix dired-omit-files regexp (Bug#35668)

* lisp/dired-x.el (dired-omit-files): Match beginning and end of
string, rather than beginning and end of line.
1 job for master in 51 minutes and 12 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1834
test-all

00:51:12

 
Name Stage Failure
failed
test-all Test
Makefile:318: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: Leaving directory '/builds/emacs/emacs/test'
make[2]: *** [check-doit] Error 1
make[1]: *** [check-expensive] Error 2
make: *** [check-expensive] Error 2
Makefile:957: recipe for target 'check-expensive' failed
ERROR: Job failed: exit code 1