Template fixes

[neerdoc]

• Fixed problem with multiple templates for different documents. This will now give an error.
• Fixed problem with doc attribute not being defined.
• Updated a bunch of the actions in the runners due to node16 going obsolete.
• Added an automation on the test coverage so that clear feedback is given to contributors if their code changes are not covered by tests.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (ee89a99) 96.27% compared to head (f258ae8) 96.33%.
Report is 1 commits behind head on develop.

Files	Patch %	Lines
doorstop/core/publishers/base.py	93.75%	0 Missing and 1 partial ⚠️

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #629      +/-   ##
===========================================
+ Coverage    96.27%   96.33%   +0.06%     
===========================================
  Files           41       41              
  Lines         5151     5158       +7     
  Branches      1210      966     -244     
===========================================
+ Hits          4959     4969      +10     
+ Misses         121      117       -4     
- Partials        71       72       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.