Merge pull request #2003 from larrybradley/remove-ubuntu-20.04

Use ubuntu-latest instead of deprecated 20.04

Author: larrybradley

.github/workflows/ci_cron_weekly.yml

@@ -67,7 +67,7 @@ jobs:
     # we include them just in the weekly cron. These also serve as a test
     # of using system libraries and using pytest directly.
 
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     name: More architectures
     if: (github.repository == 'astropy/photutils' && (github.event_name == 'schedule' || github.event_name == 'push' || github.event_name == 'workflow_dispatch' || contains(github.event.pull_request.labels.*.name, 'Arch CI')))
     env: