Fix oneof with String

[andrzejressel]

Closes #563

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.

Project coverage is 82.54%. Comparing base (1cd7896) to head (c4d15c4).

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
pulumi_wasm_generator_lib/src/schema.rs	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #569      +/-   ##
==========================================
+ Coverage   82.52%   82.54%   +0.02%     
==========================================
  Files          31       31              
  Lines        3554     3570      +16     
==========================================
+ Hits         2933     2947      +14     
- Misses        621      623       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.