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-type: direct:production
  update-type: version-update:semver-major
...

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

.github/workflows/main.yml

@@ -37,7 +37,7 @@ jobs:
           username: ${{ github.actor }}
           password: ${{ secrets.GITHUB_TOKEN }}
       - name: Build and push
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ${{ matrix.image-name }}
           push: ${{ github.event_name == 'push' && github.repository == 'DIRACGrid/container-images' && github.ref_name == 'main' }}
@@ -64,7 +64,7 @@ jobs:
 
       - name: Build base
         id: build_base
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: base
           outputs: type=oci,dest=output-base.tar
@@ -76,7 +76,7 @@ jobs:
           tar -C output-base -xf output-base.tar
 
       - name: Build services-base
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: services-base
           build-contexts: |
@@ -90,7 +90,7 @@ jobs:
           tar -C output-services-base -xf output-services-base.tar
 
       - name: Build client-base
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: client-base
           build-contexts: |