enable qemu on docker for test-cross

Author: davidhewitt

.github/workflows/ci.yml

@@ -256,6 +256,7 @@ jobs:
         # need cross HEAD for https://github.com/cross-rs/cross/issues/1645
         # will probably be ok to use released cross from 0.3
         run: cargo install cross --git https://github.com/cross-rs/cross
+      - uses: docker/setup-qemu-action@v3
       - run: pip install nox
       - run: nox -s test-cross