Fix Storybook for FOSS

Don't check for ee/ stories in FOSS

storybook/config/main.js

 /* eslint-disable import/no-commonjs */
+const IS_EE = require('../../config/helpers/is_ee_env');
+
 module.exports = {
   stories: [
     '../../app/assets/javascripts/**/*.stories.js',
-    '../../ee/app/assets/javascripts/**/*.stories.js',
-  ],
+    IS_EE && '../../ee/app/assets/javascripts/**/*.stories.js',
+  ].filter(Boolean),
   addons: ['@storybook/addon-essentials', '@storybook/addon-a11y'],
 };