Fixes #54899: Do not attempt to use real css loader in mocha unit tests

test/all.js

@@ -49,6 +49,7 @@ function main() {
 		nodeMain: __filename,
 		baseUrl: path.join(path.dirname(__dirname), 'src'),
 		paths: {
+			'vs/css': '../test/css.mock',
 			'vs': `../${ out }/vs`,
 			'lib': `../${ out }/lib`,
 			'bootstrap': `../${ out }/bootstrap`