fix: return mypy-extensions to main deps

[alexhook]

PR checklist

• I've written good commit message for all commits
• I've split changes into separate commits where it's appropriate
• I've added the description of function to documentation
• I've updated project version in pyproject.toml
• I'll make a release when PR is merged
• I'll bump pybotx in bot-template

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (5fb0552) to head (8f167c3).

❗ Current head 8f167c3 differs from pull request most recent head 4de2dd9

Please upload reports for the commit 4de2dd9 to get more accurate results.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #472   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          119       119           
  Lines         4063      4063           
  Branches       359       359           
=========================================
  Hits          4063      4063           

Flag	Coverage Δ
unittests	100.00% <ø> (ø)

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