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/build_dealii_master.yml

@@ -32,7 +32,7 @@ jobs:
           password: ${{ secrets.DOCKER_HUB_LOGIN }}
 
       - name: Build and push Docker image for main
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./contrib/docker/tester/
           cache-from: type=registry,ref=ubuntu:20.04

.github/workflows/build_dealii_master_clang.yml

@@ -32,7 +32,7 @@ jobs:
           password: ${{ secrets.DOCKER_HUB_LOGIN }}
 
       - name: Build and push Docker image for main
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./contrib/docker/tester-clang
           cache-from: type=registry,ref=ubuntu:24.04

.github/workflows/docker.yml

@@ -48,7 +48,7 @@ jobs:
 
       - name: Build and push Docker image for main
         if: contains(github.event_name, 'push')
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./contrib/docker/docker/
           cache-from: type=registry,ref=ubuntu:22.04
@@ -61,7 +61,7 @@ jobs:
 
       - name: Build and push Docker image for release
         if: contains(github.event_name, 'release')
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./contrib/docker/docker/
           cache-from: type=registry,ref=ubuntu:22.04
@@ -100,7 +100,7 @@ jobs:
 
       - name: Build and push Docker image for main
         if: contains(github.event_name, 'push')
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./contrib/docker/docker_tacc/
           cache-from: type=registry,ref=ubuntu:22.04
@@ -113,7 +113,7 @@ jobs:
 
       - name: Build and push Docker image for release
         if: contains(github.event_name, 'release')
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           context: ./contrib/docker/docker_tacc/
           cache-from: type=registry,ref=ubuntu:22.04