Pin ubuntu 22.04 for minikube setup action

The `ubuntu-latest` runner label is moving to 24.04, see https://github.blog/changelog/2024-09-25-actions-new-images-and-ubuntu-latest-changes/

Fixes https://github.com/galaxyproject/galaxy/actions/runs/11260477825/job/31317049837?pr=18963:
```
No VM guests are running outdated hypervisor (qemu) binaries on this host.
/usr/bin/lsb_release --short --codename
noble
Error: Unexpected HTTP response: 404
```

.github/workflows/integration.yaml

@@ -25,7 +25,7 @@ concurrency:
 jobs:
   test:
     name: Test
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix: