Fix oneof type name in nested message

[goccy]

SSIA

[github-actions]

Code Metrics Report

	main (1e33222)	#251 (c5181ec)	+/-
Coverage	66.4%	66.4%	0.0%
Code to Test Ratio	1:0.4	1:0.4	+0.0
Test Execution Time	7m55s	8m11s	+16s

Details

  |                     | main (1e33222) | #251 (c5181ec) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          66.4% |          66.4% | 0.0% |
  |   Files             |             76 |             76 |    0 |
  |   Lines             |          12632 |          12632 |    0 |
  |   Covered           |           8384 |           8384 |    0 |
+ | Code to Test Ratio  |          1:0.4 |          1:0.4 | +0.0 |
  |   Code              |          39413 |          39413 |    0 |
+ |   Test              |          15413 |          15418 |   +5 |
- | Test Execution Time |          7m55s |          8m11s | +16s |

Code coverage of files in pull request scope (79.4% → 79.4%)

Files	Coverage	+/-
generator/code_generator.go	79.4%	0.0%

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Reported by octocov