Update docker/build-push-action action to v7

| datasource  | package                  | from | to |
| ----------- | ------------------------ | ---- | -- |
| github-tags | docker/build-push-action | v6   | v7 |


Signed-off-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -63,7 +63,7 @@ jobs:
 
       - name: Build (no push)
         if: ${{ github.ref_name != 'main' }}
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: .
           platforms: ${{ matrix.platform.platform }}
@@ -81,7 +81,7 @@ jobs:
       - name: Build and push (main only)
         id: build_push
         if: ${{ github.ref_name == 'main' }}
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: .
           platforms: ${{ matrix.platform.platform }}