Self-hosted Google Fonts are not preloaded with Remove Unused CSS when the HTTPS protocol is missing

[johan-las]

Describe the bug
When Google Fonts are included without the HTTPS protocol and the 'Self-host Google Fonts' option is enabled along with the 'Remove Unused CSS' option, the non-self-hosted fonts are preloaded instead.

Here is an example of code that triggers this issue:

<link href="//fonts.googleapis.com/css?family=Lato:100,100italic,300,300italic,400,400italic,700,700italic,900,900italic&amp;subset=latin,latin-ext" rel="stylesheet" type="text/css">

Once we add the HTTPS protocol, self-hosted fonts were preloaded.

To Reproduce
Steps to reproduce the behavior:

1. Add a Google fonts CSS without the HTTPS protocol.
2. Add a CSS font-family using the Google fonts to an HTML element.
3. Clear the Used CSS of the testing page.
4. See the preload fonts, the Google fonts are loaded from https://fonts.gstatic.com

Expected behavior
We should preload the Self-hosted fonts.

Screenshots
Without the HTTPS protocol:

With the HTTPS protocol:

Additional context

Slack discussion: https://wp-media.slack.com/archives/C07PZNW7BJ5/p1737643980094689
HelpScout ticket: https://secure.helpscout.net/conversation/2823761415/535995?viewId=8127840