ci: exclude some test files from coverage report

[mboersma]

Reason for Change:

Adds some mock implementations and test code to codecov's exclusion list.

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #1160 into master will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1160      +/-   ##
==========================================
- Coverage   74.91%   74.73%   -0.18%     
==========================================
  Files         131      129       -2     
  Lines       18458    18325     -133     
==========================================
- Hits        13828    13696     -132     
+ Misses       3837     3836       -1     
  Partials      793      793

[CecileRobertMichon]

-0.18%

?? 🤔

[mboersma]

I think we were actually benefitting from including these files in the coverage report. Since they are the tests, their "test coverage" was probably close to 100%.

[jackfrancis]

/lgtm

[acs-bot]

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