CI: Update package tests to Ubuntu 22.04 runner

Ubuntu 20.04 runner image is deprecated in February,
and fully unsupported in April.

Also maybe the 22.04 image will be unaffected by whatever issue
prevents installing Pulsar in the latest Ubutnu 20.04 Runner image
new from this month (January)?

.github/workflows/package-tests-linux.yml

@@ -12,7 +12,7 @@ jobs:
     if: |
       !startsWith(github.event.pull_request.title, '[skip-ci]') &&
       !startsWith(github.event.pull_request.title, '[skip-package-ci]')
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
     - name: Checkout the latest code
       uses: actions/checkout@v4