fix(gen): check enum value type before generating

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 42.85714% with 28 lines in your changes missing coverage. Please review.

Project coverage is 72.74%. Comparing base (34afe31) to head (e2dc75e). Report is 20 commits behind head on main.

Files with missing lines	Patch %	Lines
gen/schema_gen_primitive.go	41.86%	23 Missing and 2 partials :warning:
gen/schema_gen.go	50.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1322 +/- ## ========================================== - Coverage 73.92% 72.74% -1.18% ========================================== Files 189 190 +1 Lines 12855 13096 +241 ========================================== + Hits 9503 9527 +24 - Misses 2804 3017 +213 - Partials 548 552 +4 ```

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