⏪️ revert: use ttf serif font for compatibility

sass/main.scss

@@ -30,7 +30,7 @@
 
 @font-face {
     src: local('Source Serif'),
-        url('fonts/SourceSerif4Variable-Roman.otf.woff2') format("woff2");
+        url('fonts/SourceSerif4Variable-Roman.ttf.woff2') format("woff2");
     /* Copyright 2014 - 2023 Adobe (http://www.adobe.com/), with Reserved Font Name ‘Source’.adobe.com/). Licensed under the SIL Open Font License, Version 1.1. More information available at: http://scripts.sil.org/OFL */
     font-family: 'Source Serif';
     font-display: swap;