Revert "Bump docker/build-push-action from 5 to 6 (#7850)" (#7898)

This reverts commit 3d84ad6.

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### Description of the change

Reverts the previous bump of GitHub action docker/build-push-action (6
-> 5).
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### Benefits

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The CI works again.

### Possible drawbacks

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### Applicable issues

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- fixes #

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.github/workflows/kubeapps-general.yaml

@@ -286,7 +286,7 @@ jobs:
       - uses: docker/setup-qemu-action@v3
       - uses: docker/setup-buildx-action@v3
       - name: Build image
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v5
         with:
           file: cmd/${{matrix.image}}/Dockerfile
           platforms: ${{ env.IMG_PLATFORMS }}
@@ -323,7 +323,7 @@ jobs:
       - uses: docker/setup-qemu-action@v3
       - uses: docker/setup-buildx-action@v3
       - name: Build image
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v5
         with:
           context: dashboard
           platforms: ${{ env.IMG_PLATFORMS }}
@@ -359,7 +359,7 @@ jobs:
           tags: ${{needs.setup.outputs.img_dev_tag}}
       - uses: docker/setup-buildx-action@v3
       - name: Build image
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v5
         with:
           context: integration
           # It doesn't make sense investing CI time in making a multiplatform image here