fix: correctly generate array when items are a oneOf array with length 1

[mrlubos]

Closes https://github.com/hey-api/openapi-ts/issues/1258

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🦋 Changeset detected

Latest commit: d60d260342ff3013c2e228151e9b897224eb89cc

The changes in this PR will be included in the next version bump.

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Codecov Report

Attention: Patch coverage is 70.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 67.63%. Comparing base (f31d4e2) to head (d60d260). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
...ages/openapi-ts/src/openApi/3.0.x/parser/schema.ts	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1266 +/- ## ======================================= Coverage 67.63% 67.63% ======================================= Files 132 132 Lines 19682 19684 +2 Branches 1773 1775 +2 ======================================= + Hits 13311 13314 +3 + Misses 6367 6366 -1 Partials 4 4 ``` | [Flag](https://app.codecov.io/gh/hey-api/openapi-ts/pull/1266/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=hey-api) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/hey-api/openapi-ts/pull/1266/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=hey-api) | `67.63% <70.00%> (+<0.01%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=hey-api#carryforward-flags-in-the-pull-request-comment) to find out more.

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