📌 Pin Github actions runners to 22.04

The end-to-end tests otherwise require a playwright upgrade which we've
done on master, but for these maintenance branches we can just pin to
old runner versions to immediately fix the problem.

(cherry picked from commit b4224e0)

.github/workflows/ci.yml

@@ -195,7 +195,7 @@ jobs:
       - uses: ./.github/actions/report-flaky
 
   e2etests:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix: