Disable enable-local-variables for hunk-only in diff-syntax-fontify-props

* lisp/vc/diff-mode.el (diff-syntax-fontify-props): Let-bind
enable-local-variables to nil when hunk-only is non-nil (bug#39190)
1 job for master in 57 minutes and 21 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #5349
test-all

00:57:21