ci(deps): bump docker/build-push-action from 5 to 6

Bumps [docker/build-push-action](https://github.com/docker/build-push-action) from 5 to 6.
- [Release notes](https://github.com/docker/build-push-action/releases)
- [Commits](docker/build-push-action@v5...v6)

---
updated-dependencies:
- dependency-name: docker/build-push-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -110,7 +110,7 @@ jobs:
       uses: docker/setup-buildx-action@v3
 
     - name: Build Docker image
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: .
         push: false

.github/workflows/release.yml

@@ -31,7 +31,7 @@ jobs:
         uv run pytest tests/ -v
 
     - name: Build Docker image
-      uses: docker/build-push-action@v5
+      uses: docker/build-push-action@v6
       with:
         context: .
         push: false