Warn on empty config

[janosh]

Closes #499.

This PR is closely inspired by materialsproject/jobflow#415. Thanks @mcgalcode! 👍

[janosh]

@utf Could you run this shell command?

gh api -i repos/materialsproject/atomate2/branches/main/protection/required_status_checks --method PATCH --input - <<<"$(gh api repos/materialsproject/atomate2/commits/7d16877/check-runs --paginate --jq '{ context: .check_runs[].name }' | jq -s '{ checks: . | unique }')"

Requires brew install gh. It will set all GitHub Actions that triggered for the latest commit of this PR as required status checks. Allows contributors like me to set PRs to auto-merge once all checks are green.

[codecov]

Codecov Report

Merging #522 (7d16877) into main (c4f1cb0) will increase coverage by 0.21%.
Report is 6 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #522      +/-   ##
==========================================
+ Coverage   75.04%   75.26%   +0.21%     
==========================================
  Files          74       74              
  Lines        6572     6577       +5     
  Branches      952      953       +1     
==========================================
+ Hits         4932     4950      +18     
+ Misses       1340     1327      -13     
  Partials      300      300              

Files Changed	Coverage Δ
src/atomate2/settings.py	100.00% <100.00%> (+4.25%)	⬆️

... and 1 file with indirect coverage changes