Downgrade ubuntu back to 22.04.

I'm getting issues with 24.04 where pak installs some system packages
with apt-get, some system services are upgraded and restarted and the CI
runner is canceled. Not sure what the reason is, but 22.04 doesn't have
this problem.

.github/workflows/touchstone.yaml

@@ -77,9 +77,9 @@ jobs:
     permissions:
       contents: read
 
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-22.04
     env:
-      RSPM: "https://packagemanager.posit.co/cran/__linux__/noble/2024-05-15"
+      RSPM: "https://packagemanager.posit.co/cran/__linux__/jammy/2024-05-15"
       R_REMOTES_NO_ERRORS_FROM_WARNINGS: true
       GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}