Bug fix: regex started with /= parsed as AssignDiv

[Nikita-str]

This Pull Request closes #3329

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 52.94%. Comparing base (6ddc2b4) to head (2db3be3).
Report is 295 commits behind head on main.

Files with missing lines	Patch %	Lines
core/parser/src/lexer/mod.rs	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4048      +/-   ##
==========================================
+ Coverage   47.24%   52.94%   +5.70%     
==========================================
  Files         476      483       +7     
  Lines       46892    46952      +60     
==========================================
+ Hits        22154    24859    +2705     
+ Misses      24738    22093    -2645     

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