fix: revert to unescaped regex capture grouping in workflow:rules

The workflow:rules use Ruby regex. The scripts use Bash regex. The escaping rules for parentheses and pipes in groups and captures are different...

.gitlab-ci.yml

@@ -63,8 +63,8 @@ workflow:
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
     - if: '$CI_PIPELINE_SOURCE == "web"'
     - if: '$CI_COMMIT_BRANCH == "master"'
-    - if: '$CI_COMMIT_BRANCH =~ /^v[0-9]+\.[0-9]+-\(alpha\|beta\|stable\)/'          ## main stable branch: vX.Y-stable
-    - if: '$CI_COMMIT_BRANCH =~ /^v[0-9]+\.[0-9]+-[a-z]+-\(alpha\|beta\|stable\)/'   ## special stable branch: vX.Y-acadia-stable (etc)
+    - if: '$CI_COMMIT_BRANCH =~ /^v[0-9]+\.[0-9]+-(alpha|beta|stable)/'          ## main stable branch: vX.Y-stable
+    - if: '$CI_COMMIT_BRANCH =~ /^v[0-9]+\.[0-9]+-[a-z]+-(alpha|beta|stable)/'   ## special stable branch: vX.Y-acadia-stable (etc)
     - if: '$CI_COMMIT_TAG =~ /^v[0-9]+\.[0-9]+\.[0-9]+/'            ## commit tags start with vX.Y.Z with optional suffix
 
 ## plan: