Add filters to only calculate coverage for relevant files

[etagwerker]

• Add an entry to CHANGELOG.md that links to this PR under the "main (unreleased)" heading.

Description:

This improves the SimpleCov configuration to only track relevant files.

✅ I will abide by the code of conduct.

[codecov]

Codecov Report

Merging #108 (59e669f) into main (440428d) will increase coverage by 0.13%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #108      +/-   ##
==========================================
+ Coverage   98.27%   98.41%   +0.13%     
==========================================
  Files          25       17       -8     
  Lines         465      315     -150     
==========================================
- Hits          457      310     -147     
+ Misses          8        5       -3     

Impacted Files	Coverage Δ
test/lib/skunk/cli/options/argv_test.rb
lib/skunk/version.rb
test/lib/skunk/cli/commands/version_test.rb
test/lib/skunk/rubycritic/analysed_module_test.rb
test/lib/skunk/cli/commands/help_test.rb
test/lib/skunk/cli/commands/compare_score_test.rb
...est/lib/skunk/cli/commands/status_reporter_test.rb
test/lib/skunk/cli/commands/compare_test.rb

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