actually switch to QEMU to be able to use multi-platform builds

multi-platform builds were introduced in r119557e but we actually
need the QEMU based driver on github to work with that

Signed-off-by: Felix Kronlage-Dammers <fkr@hazardous.org>

Author: fkr

.github/workflows/build-docker.yml

@@ -24,6 +24,12 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v3
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
       - name: Log in to the Container registry
         uses: docker/login-action@v3
         with: