test: add build date label

.gitea/workflows/build-and-push.yaml

@@ -9,6 +9,9 @@ jobs:
     name: Build image
     runs-on: ubuntu-latest
     steps:
+    - name: Get current date
+      id: date
+      run: echo "::set-output name=date::$(date '+%Y-%m-%dT%TZ%z')"
     - uses: actions/checkout@v3
     - uses: docker/metadata-action@v3
       id: metadata
@@ -25,3 +28,5 @@ jobs:
         tags: latest
         labels: ${{ steps.metadata.outputs.labels }}
         cache: false
+        build-args: |
+          BUILD_DATE: ${{ steps.date.outputs.date }}