Restore EKAT nightly testing

[jgfouca]

The Jenkins scripts used to enable EKAT testing for nightly runs:

  if [ -n "$PULLREQUESTNUM" ]; then
      is_at_run=1
  else
      TAS_ARGS="${TAS_ARGS} --test-level nightly"
      # We never want to submit a fake run to the dashboard                                                                                                                                                                    
      if [ -z "$SCREAM_FAKE_ONLY" ]; then
          # Run EKAT tests for real nightly runs                                                                                                                                                                               
          TAS_ARGS="${TAS_ARGS} --submit -c EKAT_ENABLE_TESTS=ON"
      fi
  fi

It looks like we also lost the --test-level nightly flag. Looking around eamxx, it looks like the cmake setting SCREAM_TEST_LEVEL is not really used for much, so maybe this is fine for now.

This PR will re-enable EKAT testing for scheduled runs (nightlies). I'd also like to enable them when the EKAT label is present on a PR is present, but that seems to be pretty hard to do in the YAML.

Also, remove trailing whitespace in a few places.

[BFB]

[bartgol]

This is the best way to get things going, though I may suggest we write a separate workflow file for ekat's testing. The separate workflow can be triggered by PRs if the ekat submodule is modified, and can also take care of nightly testing.

Re: labels. When I first started working on the AT2 yaml files, I did add support for doing different things depending on labels (e.g., to skip some jobs). However, that made the files much more complicated.