Add fixtures path to Jest config

jest.config.js

@@ -18,6 +18,7 @@ module.exports = {
   moduleNameMapper: {
     '^~(.*)$': '<rootDir>/app/assets/javascripts$1',
     '^ee(.*)$': '<rootDir>/ee/app/assets/javascripts$1',
+    '^fixtures(.*)$': '<rootDir>/spec/javascripts/fixtures$1',
     '^helpers(.*)$': '<rootDir>/spec/frontend/helpers$1',
     '^vendor(.*)$': '<rootDir>/vendor/assets/javascripts$1',
     '\\.(jpg|jpeg|png|svg)$': '<rootDir>/spec/frontend/__mocks__/file_mock.js',