build: update nightly workflow

- docker/build-push-action to v4
- Drop `platforms` from `docker/setup-qemu-action` step, as this is
  the default.

Signed-off-by: Hidde Beydals <hidde@hhh.computer>

.github/workflows/nightly.yml

@@ -17,15 +17,13 @@ jobs:
       - uses: actions/checkout@v3
       - name: Setup QEMU
         uses: docker/setup-qemu-action@v2
-        with:
-          platforms: all
       - name: Setup Docker Buildx
         id: buildx
         uses: docker/setup-buildx-action@v2
         with:
           buildkitd-flags: "--debug"
       - name: Build multi-arch container image
-        uses: docker/build-push-action@v3
+        uses: docker/build-push-action@v4
         with:
           push: false
           builder: ${{ steps.buildx.outputs.name }}