Use registry PAT for Gitea Docker login

.gitea/workflows/docker-build.yml

@@ -6,14 +6,12 @@ on:
 
 env:
   REGISTRY: git.mischlabs.de
+  REGISTRY_USER: MrDiderot
   REGISTRY_IMAGE: git.mischlabs.de/mrdiderot/michess
 
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
-    permissions:
-      contents: read
-      packages: write
     steps:
       - name: Checkout
         uses: actions/checkout@v4
@@ -46,7 +44,12 @@ jobs:
       - name: Log in to Gitea Package Registry
         shell: sh
         run: |
-          echo "${{ gitea.token }}" | docker login "${{ env.REGISTRY }}" -u "${{ gitea.actor }}" --password-stdin
+          if [ -z "${{ secrets.REGISTRY_TOKEN }}" ]; then
+            echo "Missing REGISTRY_TOKEN secret."
+            echo "Create a Gitea personal access token for MrDiderot with package Read and Write permission."
+            exit 1
+          fi
+          echo "${{ secrets.REGISTRY_TOKEN }}" | docker login "${{ env.REGISTRY }}" -u "${{ env.REGISTRY_USER }}" --password-stdin
 
       - name: Build and push Docker image
         shell: sh