workflow: use qemu-user-static with openat2 patches

This commit adds the https://launchpad.net/~mvo/+archive/ubuntu/qemu/
PPA that contains a backport of the openat2 patches for qemu-9 so
that we can test cross-arch building again.

.github/workflows/tests.yml

@@ -94,6 +94,11 @@ jobs:
         curl -fsSL $key_url | gpg --dearmor | sudo tee /etc/apt/trusted.gpg.d/devel_kubic_libcontainers_unstable.gpg > /dev/null
         sudo apt update
         sudo apt install -y podman skopeo
+        # get qemu-9 with openat2 patches
+        sudo apt install -y software-properties-common
+        sudo apt-add-repository -y ppa:mvo/qemu
+        sudo apt update
+        sudo apt install -y qemu-user-static
     - name: Install python test deps
       run: |
         # make sure test deps are available for root