Refactorings related to ExitCode.

[tobiasraabe]

Changes

Provide a description and/or bullet points to describe the changes in this PR.

Todo

• Reference issues which can be closed due to this PR with "Closes #x".
• Review whether the documentation needs to be updated.
• Document PR in docs/changes.rst.

[codecov]

Codecov Report

Merging #188 (056b9da) into main (13aac48) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #188      +/-   ##
==========================================
+ Coverage   92.83%   92.85%   +0.01%     
==========================================
  Files          72       71       -1     
  Lines        6673     6688      +15     
==========================================
+ Hits         6195     6210      +15     
  Misses        478      478              

Flag	Coverage Δ
end_to_end	79.20% <98.63%> (+0.04%)	⬆️
integration	42.18% <41.09%> (+0.12%)	⬆️
unit	68.80% <42.46%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/_pytask/live.py	99.36% <ø> (ø)
src/_pytask/logging.py	88.00% <ø> (ø)
src/pytask/__init__.py	100.00% <ø> (ø)
src/_pytask/build.py	92.85% <100.00%> (ø)
src/_pytask/clean.py	90.90% <100.00%> (ø)
src/_pytask/collect_command.py	87.71% <100.00%> (ø)
src/_pytask/graph.py	75.49% <100.00%> (ø)
src/_pytask/mark/__init__.py	96.45% <100.00%> (ø)
src/_pytask/outcomes.py	90.12% <100.00%> (+1.08%)	⬆️
src/_pytask/profile.py	86.81% <100.00%> (ø)
... and 16 more

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