Quote asterisks in documentation workflow

Yaml strings containing asterisks require quoting, because asterisks have
special meaning otherwise.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

.github/workflows/documentation.yml

@@ -5,13 +5,13 @@ on:
   push:
     branches:
       - main
-      - v4.*.x
+      - 'v4.*.x'
     paths:
       - 'userdocs/**'
   pull_request:
     branches:
       - main
-      - v4.*.x
+      - 'v4.*.x'
     paths:
       - 'userdocs/**'