[Security] Fix locale-sensitive header redaction

[gonzaloriestra]

WHY are these changes introduced?

Redaction of sensitive headers (like `AUTHORIZATION`) could be bypassed on systems with certain locales (e.g., Turkish) because `toLocaleLowerCase()` is non-deterministic for ASCII characters like 'I' (which becomes 'ı' in Turkish).

WHAT is this pull request doing?

This PR replaces `toLocaleLowerCase()` with `toLowerCase()` in `sanitizedHeadersOutput` to ensure consistent ASCII-based matching for HTTP headers regardless of the user's locale. It also adds a regression test that simulates the problematic locale behavior.

How to test your changes?

CI

Post-release steps

None.

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — I've identified the correct bump type (`patch` for bug fixes · `minor` for new features · `major` for breaking changes) and added a changeset with `pnpm changeset add`

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PR created automatically by Jules for task 14224719727929470904 started by @gonzaloriestra

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