refactor(cli): extract unknown args validation into a function

[bearomorphism]

[codecov[bot]]

Codecov Report

:x: Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review. :warning: Please upload report for BASE (v4-10-1@6c8fad1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
commitizen/cli.py	63.63%	4 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             v4-10-1    #1688   +/-   ##
==========================================
  Coverage           ?   98.67%           
==========================================
  Files              ?       60           
  Lines              ?     2648           
  Branches           ?        0           
==========================================
  Hits               ?     2613           
  Misses             ?       35           
  Partials           ?        0           

Flag	Coverage Δ
unittests	98.67% <63.63%> (?)

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