ci(versions): skip existing-versions-check on release-please branches

Author: blakeli0

.github/workflows/versions.yaml

@@ -34,8 +34,8 @@ jobs:
   existing-versions-check:
     runs-on: ubuntu-latest
     if: |
-      github.repository_owner == 'googleapis' && github.head_ref == 'release-please--branches--main' &&
-      !endsWith(github.event.pull_request.title, 'SNAPSHOT')
+      github.repository_owner == 'googleapis' &&
+      !startsWith(github.head_ref, 'release-please')
     steps:
     - run: sudo apt-get update -y
     - run: sudo apt-get install libxml2-utils