refactor(yaml): simplify isWhiteSpaceOrEOL

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 68.75000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 95.74%. Comparing base (ba704da) to head (1c55f45).

Files	Patch %	Lines
yaml/_loader.ts	68.75%	5 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #5271 +/- ## ========================================== - Coverage 95.74% 95.74% -0.01% ========================================== Files 458 458 Lines 37973 37969 -4 Branches 5562 5561 -1 ========================================== - Hits 36356 36352 -4 Misses 1576 1576 Partials 41 41 ```

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