dialects: (varith) fix switch parsing

[alexarice]

Apparently putting generic syntax in a roundtrip test never tests the parsing.
Should have listened to @superlopuh

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.10%. Comparing base (21b6a60) to head (4a1b2e2).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3351      +/-   ##
==========================================
+ Coverage   90.06%   90.10%   +0.03%     
==========================================
  Files         447      447              
  Lines       56532    56533       +1     
  Branches     5425     5425              
==========================================
+ Hits        50915    50938      +23     
+ Misses       4184     4162      -22     
  Partials     1433     1433              

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