tests: search-input: use render helper

Ember's this.render method and @ember/test-helpers's render method are
equivalent, but using @ember/test-helpers' render method is the
recommended approach. As such, let's go ahead and switch this over.

While we're here, let's re-enable this eslint rule as we no longer have
any violations.

.eslintrc.js

@@ -24,7 +24,6 @@ module.exports = {
     'ember/no-new-mixins': 'off',
     'ember/no-mixins': 'off',
     'ember/require-tagless-components': 'off',
-    'ember/no-test-this-render': 'off',
     'ember/no-classic-classes': 'off',
     'ember/no-get': 'off',
     'ember/no-classic-components': 'off',

tests/integration/components/search-input-test.js

@@ -1,6 +1,6 @@
 import { module, test } from 'qunit';
 import { setupRenderingTest } from 'ember-qunit';
-import { fillIn, waitFor } from '@ember/test-helpers';
+import { fillIn, render, waitFor } from '@ember/test-helpers';
 import hbs from 'htmlbars-inline-precompile';
 import { set } from '@ember/object';
 
@@ -155,7 +155,7 @@ module('Integration | Component | search input', function (hooks) {
       ];
     });
 
-    await this.render(hbs`{{search-input}}`);
+    await render(hbs`{{search-input}}`);
 
     await fillIn('#search-input', 'model');
 
@@ -171,7 +171,7 @@ module('Integration | Component | search input', function (hooks) {
       return [];
     });
 
-    await this.render(hbs`{{search-input}}`);
+    await render(hbs`{{search-input}}`);
 
     await fillIn('#search-input', 'model');