Describe the bug
Fonts using @import are not preloaded.

To Reproduce
Steps to reproduce the behavior:

1. Install and activate WPR 3.19.
2. Enable Preload Fonts & Self-host Google Fonts.
3. Visit page template using GF above the fold via @import ( i.e. https://rocketlabsqa.ovh/preloadfonts_import/, preloadfonts_import.php template).
4. Clear the cache and revisit the page.

Expected behavior
Above the fold fonts using @import should be preloaded, too.

Note: Issue related to #7241 .

Screenshots
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