fix: skip version file updates on main for pre-release tags (#1396)

When a pre-release is created (e.g. v12.1.0-alpha.1), the release
workflow was updating Chart.yaml, kustomization.yaml, and other version
files on main with the pre-release version string. This is undesirable
because main should only reference stable release versions.

Add a !contains(github.event.release.tag_name, '-') guard to the
prepare-release job, matching the convention already used in publish.yaml
and release-manifests.yaml.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: chris-rock

.github/workflows/release.yaml

@@ -10,8 +10,8 @@ on:
 jobs:
   prepare-release:
     runs-on: ubuntu-latest
-    # Only run for version tags
-    if: startsWith(github.event.release.tag_name, 'v')
+    # Only run for stable version tags (skip pre-releases like v1.0.0-alpha.1)
+    if: startsWith(github.event.release.tag_name, 'v') && !contains(github.event.release.tag_name, '-')
     permissions:
       contents: write