fix: use GITEA_TOKEN for GHCR login in Gitea Actions

Replace ${{ secrets.GITHUB_TOKEN }} with ${{ secrets.GITEA_TOKEN }}
for docker/login-action in Gitea Actions. GITHUB_TOKEN is not available
in Gitea Actions and was causing 'authentication required' failures for
ghcr.io push, leaving the auth service with a stale image on UAT.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.github/workflows/ci.yml

@@ -47,7 +47,7 @@ jobs:
         with:
           registry: ${{ env.REGISTRY }}
           username: ${{ github.actor }}
-          password: ${{ secrets.GITHUB_TOKEN }}
+          password: ${{ secrets.GITEA_TOKEN }}
 
       - name: Extract metadata
         id: meta