ci: set up qemu only when needed

Author: vlaci

.github/workflows/build-publish-image.yml

@@ -51,6 +51,7 @@ jobs:
             type=sha
 
       - name: Set up QEMU
+        if: matrix.platform != 'linux/amd64'
         uses: docker/setup-qemu-action@v3
 
       - name: Set up Docker Buildx