Font Library: replace all references to 6.4.0 by 6.5.0

## What?
Replace all references to 6.4.0 by 6.5.0 in the font library codebase.

Example from function comments:
```php
	/**
	 * Gets the upload directory for fonts.
	 *
	 * @since 6.4.0
	 *
	 * @return
 ```

## Why?
Because the feature was punted from WordPress core 6.4.0 to 6.5.0.