ci: switch qemu-user-static setup to fix setuid

Problem: flux-sched side ran into issues with setuid binaries in some
cases under aarch64 emulation building containers.  It seems to depend
on which workers pick up the job, so seems best to bring the solution
over.

Solution: Run the docker container with the setup script directly with
the appropriate option to handle setuid credentials.

.github/workflows/main.yml

@@ -154,9 +154,9 @@ jobs:
       uses: docker/setup-buildx-action@v2
       if: matrix.needs_buildx
 
-    - uses: dbhi/qus/action@main
-      with:
-        targets: aarch64
+    - name: setup qemu-user-static
+      run: |
+        docker run --rm --privileged aptman/qus -s -- -p --credential aarch64
 
     - name: docker-run-checks
       env: ${{matrix.env}}