Fix tests setup

This change will allow the config to be reset after each test.

It fixes the error thrown by ember-template-lint and will fix the
floating dependencies tests.

Author: dcyriller

test/unit/rules/lint-prettier-test.js

@@ -4,7 +4,7 @@ const plugin = require("../../../ember-template-lint-plugin-prettier");
 generateRuleTests({
   name: "prettier",
 
-  groupMethodBefore: before,
+  groupMethodBefore: beforeEach,
   groupingMethod: describe,
   testMethod: it,
   plugins: [plugin],