ci: revert to auto GITEA_TOKEN for registry auth

Gitea 1.26 (PR #36173) honors permissions.packages: write on the
auto-provided GITEA_TOKEN, so the PAT workaround is no longer needed.
You can delete the REGISTRY_TOKEN org secret.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitea/workflows/helm-release.yml

@@ -31,8 +31,8 @@ jobs:
 
       - name: Log in to Gitea OCI registry
         run: |
-          echo "${{ secrets.REGISTRY_TOKEN }}" | helm registry login git.farh.net \
-            --username gitea-admin \
+          echo "${{ secrets.GITEA_TOKEN }}" | helm registry login git.farh.net \
+            --username "${{ github.actor }}" \
             --password-stdin
 
       - name: Push chart to Gitea OCI registry