Use Gitea job token for registry login

.gitea/workflows/docker-build.yml

@@ -11,6 +11,9 @@ env:
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -43,13 +46,7 @@ jobs:
       - name: Log in to Gitea Package Registry
         shell: sh
         run: |
-          if [ -z "${{ secrets.REGISTRY_USER }}" ] || [ -z "${{ secrets.REGISTRY_TOKEN }}" ]; then
+          echo "${{ gitea.token }}" | docker login "${{ env.REGISTRY }}" -u "${{ gitea.actor }}" --password-stdin
-            echo "Missing registry credentials."
-            echo "Create repository secrets REGISTRY_USER and REGISTRY_TOKEN."
-            echo "REGISTRY_TOKEN must be a Gitea access token with package write permission."
-            exit 1
-          fi
-          echo "${{ secrets.REGISTRY_TOKEN }}" | docker login "${{ env.REGISTRY }}" -u "${{ secrets.REGISTRY_USER }}" --password-stdin
 
       - name: Build and push Docker image
         shell: sh