ci: Fix docker working directory

.github/workflows/docker.yml

@@ -5,10 +5,6 @@ on:
   schedule:
     - cron: "23 5 * * *"  # daily at 5:23
 
-defaults:
-  run:
-    working-directory: scripts/dev/ci/docker/
-
 jobs:
   docker:
     runs-on: ubuntu-latest
@@ -26,6 +22,7 @@ jobs:
       - run: pip install jinja2
       - name: Generate Dockerfile
         run: python3 generate.py ${{ matrix.image }}
+        working-directory: scripts/dev/ci/docker/
       - uses: docker/setup-buildx-action@v1
       - uses: docker/login-action@v1
         with:
@@ -33,6 +30,7 @@ jobs:
           password: ${{ secrets.DOCKER_TOKEN }}
       - uses: docker/build-push-action@v2
         with:
+          file: scripts/dev/ci/docker/Dockerfile
           context: .
           tags: "qutebrowser/ci:${{ matrix.image }}"
           push: ${{ github.ref == 'refs/heads/master' }}