Ignore fonts upload folder

[ironprogrammer]

Adds the /src/wp-content/fonts directory to .gitignore, treating it like the plugins and uploads directories. The fonts upload storage location was most recently updated in WordPress/gutenberg#54122.

Discussions around where to store installed fonts can be found here, and later here.

Trac ticket: https://core.trac.wordpress.org/ticket/59166

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[swissspidy]

Fixed in https://core.trac.wordpress.org/changeset/57640