Fix CI errors around @ember/polyfills on Ember 5.3+

Author: lolmaus

tests/dummy/config/ember-try.js

@@ -52,6 +52,11 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': '~5.3.0',
+
+            // When this addon is upgraded to Ember 5.3+, this line should be moved into package.json,
+            // and instead Ember 3.x scenarios should have test-helpers fixed at 2.x
+            '@ember/test-helpers': '^2.9.3',
+            'ember-qunit': '^6.0.0',
           },
         },
       },
@@ -60,6 +65,11 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': emberReleaseVersion,
+
+            // When this addon is upgraded to Ember 5.3+, this line should be moved into package.json,
+            // and instead Ember 3.x scenarios should have test-helpers fixed at 2.x
+            '@ember/test-helpers': '^2.9.3',
+            'ember-qunit': '^6.0.0',
           },
         },
       },
@@ -68,6 +78,11 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': await getChannelURL('beta'),
+
+            // When this addon is upgraded to Ember 5.3+, this line should be moved into package.json,
+            // and instead Ember 3.x scenarios should have test-helpers fixed at 2.x
+            '@ember/test-helpers': '^2.9.3',
+            'ember-qunit': '^6.0.0',
           },
         },
       },
@@ -76,6 +91,11 @@ module.exports = async function () {
         npm: {
           devDependencies: {
             'ember-source': await getChannelURL('canary'),
+
+            // When this addon is upgraded to Ember 5.3+, this line should be moved into package.json,
+            // and instead Ember 3.x scenarios should have test-helpers fixed at 2.x
+            '@ember/test-helpers': '^2.9.3',
+            'ember-qunit': '^6.0.0',
           },
         },
       },