Skip functional tests for .gitignore update

The file itself has no functional impact.

Also add appropriate escape so that '.' is treated as a real period
strictly.

Change-Id: I9a8a7cb1e4719f6a39b70d4b3889aa0ac019650e
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

.zuul.yaml

@@ -551,9 +551,11 @@
       # Translations
       - ^.*/locale/.*po$
       # pre-commit config
-      - ^.pre-commit-config.yaml$
+      - ^\.pre-commit-config\.yaml$
+      # gitignore config
+      - ^\.gitignore$
       # gitreview config
-      - ^.gitreview$
+      - ^\.gitreview$
 
 - job:
     name: devstack-minimal