fix(ci): use direct docker login with github.token for registry auth (CAR-973)

docker/login-action@v3 fails with Gitea's automatic token.
Use direct docker login with github.token instead, which has
the necessary write:package scope for the container registry.

Related: CAR-1009 (CI registry token standardization)

.gitea/workflows/ci.yml

@@ -43,11 +43,8 @@ jobs:
           echo "version=$VERSION" >> "$GITHUB_OUTPUT"
 
       - name: Log in to Gitea Container Registry
-        uses: docker/login-action@v3
-        with:
-          registry: ${{ env.REGISTRY }}
-          username: ${{ github.actor }}
-          password: ${{ secrets.GITEA_TOKEN }}
+        run: |
+          echo "${{ github.token }}" | docker login ${{ env.REGISTRY }} --username "${{ github.actor }}" --password-stdin
 
       - name: Extract metadata
         id: meta