Fix: build your own font provider - step 3

[BuckyBuck135]

Description (required)

Following Florian's message on Discord regarding a wrong copy and paste, this PR fixes step 3 of the 'build your own font provider' section.

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en/reference/experimental-flags/fonts.mdx	Source changed, localizations will be marked as outdated.

Warnings reference

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🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

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[sarah11918]

LGTM! Thank you so much for this quick fix!

[florian-lefebvre]

Thanks!