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 :warning:

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Additional details and impacted files

```diff @@ 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 ```

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