Configure binfmt_misc for QEMU on CI

As in: https://docs.gitlab.com/omnibus/development/s390x/

Author: EliahKagan

.github/workflows/ci.yml

@@ -349,6 +349,8 @@ jobs:
         uses: taiki-e/install-action@v2
         with:
           tool: cross
+      - name: Configure binfmt_misc for QEMU
+        run: docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
       - name: Build cross image
         run: just cross-image ${{ matrix.target }}
       - name: Test (unit)