fix: Regex validation bugfix & unit test

[MelReyCG]

This regex validation bugfix fix cover the case where a regex could validate a substring of a given valid string.
As an exemple, the generated enum regex None|Default|Value|Value2, while validating Value2, can validate Value, and wrongly produced the following error:

Input string validation failed at:
  "Value2"
        ^
Expected format: Input value must be one of { None, Default, Value, Value2 }.

Thanks @paveltomin for finding it!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.79%. Comparing base (7eee999) to head (fe2a95b).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3403   +/-   ##
========================================
  Coverage    56.79%   56.79%           
========================================
  Files         1076     1076           
  Lines        95743    95749    +6     
========================================
+ Hits         54377    54383    +6     
  Misses       41366    41366           

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