Fix casing of GeoJSON/TopoJSON

[letmaik]

Why:

Fixes casing of GeoJSON/TopoJSON file formats.

What's being changed (if available, include any code snippets, screenshots, or gifs):

Casing.

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[github-actions]

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The table contains an overview of files in the content directory that have been changed in this pull request. It's provided to make it easy to review your changes on the staging site. Please note that changes to the data directory will not show up in this table.

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Content directory changes

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Source	Preview	Production	What Changed
repositories/working-with-files/using-files/working-with-non-code-files.md	fpt ghec ghes@ 3.5 3.4 3.3 3.2 ghae	fpt ghec ghes@ 3.5 3.4 3.3 3.2 ghae

[cmwilson21]

@letmaik Thanks so much for opening a PR! I'll get this triaged for review ⚡

[felicitymay]

As discussed on #19029, this change looks good.

I'll wait to hear back from you on #19029 (comment) before deciding when best to merge your two pull requests.

[github-actions]

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