.dir-locals.el: Add missing final newline

3 jobs for trivial in 8 minutes and 40 seconds
Status Job ID Name Coverage
  Docker Image
passed #685667
debian-testing

00:00:43

 
  Build And Test
passed #685668
autotools-build-and-test

00:07:56

passed #685669
meson-build-and-test

00:01:53