Update VERSION to 2.1.1

[gregschohn]

This PR updates the VERSION file to 2.1.1.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.64%. Comparing base (d45f4f3) to head (83199d7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #1201   +/-   ##
=========================================
  Coverage     80.64%   80.64%           
  Complexity     3076     3076           
=========================================
  Files           421      421           
  Lines         15610    15610           
  Branches       1053     1053           
=========================================
  Hits          12588    12588           
  Misses         2381     2381           
  Partials        641      641           

Flag	Coverage Δ
unittests	80.64% <ø> (ø)

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