fix(i18n): generate fallbacks for pages with filenames containing locale keys

[fredriknorlin]

Changes

Fixes a bug where Astro's i18n fallback system with fallbackType: 'rewrite' would not generate fallback files for pages whose filename started with a locale key.

Closes: #14359

(PS. This is my first PR in this project, so please let me know if I have missed anything)

Testing

• Added tests covering some different locale positions in both folders and pages (folder names turned out to also be affected).
• Although the fix turned out to be a oneliner, I kept the tests for future cover.

Docs

N/A: Bug fix

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Latest commit: f96090a

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[codspeed-hq]

CodSpeed Performance Report

Merging #14690 will not alter performance

_{Comparing fredriknorlin:fix/i18n-fallbacks (f96090a) with main (f657183)¹}

Summary

✅ 6 untouched

Footnotes

1. No successful run was found on main (420836c) during the generation of this report, so f657183 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩