Fix missing gitgraph css import (#12112)

The filter was wrongly excluding the gitGraph.css file. Need to clean
this up later so that imports are always relative to the source file
(which is not the case for fonts right now).

Regressed by: #11997

Co-authored-by: zeripath <art27@cantab.net>

Author: silverwind

webpack.config.js

@@ -25,6 +25,8 @@ const isProduction = process.env.NODE_ENV !== 'development';
 const filterCssImport = (parsedImport, cssFile) => {
   const url = parsedImport && parsedImport.url ? parsedImport.url : parsedImport;
   const importedFile = url.replace(/[?#].+/, '').toLowerCase();
+  if (/vendor\/assets/.test(url)) return false; // font imports
+  if (/web_src[/\\]less/.test(cssFile)) return true; // relative imports
   if (cssFile.includes('monaco')) return true;
   if (cssFile.includes('fomantic')) {
     if (/brand-icons/.test(importedFile)) return false;