Update docker/build-push-action to v6 (#8)

* Update `docker/build-push-action` to `v6`

* Update gha-publish-chart.yaml

Author: 0xiso

.github/workflows/gha-publish-chart.yaml

@@ -76,12 +76,6 @@ jobs:
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v3
-        with:
-          # Pinning v0.9.1 for Buildx and BuildKit v0.10.6
-          # BuildKit v0.11 which has a bug causing intermittent
-          # failures pushing images to GHCR
-          version: v0.9.1
-          driver-opts: image=moby/buildkit:v0.10.6
 
       - name: Login to GitHub Container Registry
         uses: docker/login-action@v3
@@ -91,7 +85,7 @@ jobs:
           password: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Build & push controller image
-        uses: docker/build-push-action@v5
+        uses: docker/build-push-action@v6
         with:
           file: Dockerfile
           platforms: linux/amd64,linux/arm64