add script to force testing against all versions of ember

Author: lobsterkatie

packages/ember/package.json

@@ -27,6 +27,7 @@
     "postpublish": "ember ts:clean",
     "start": "ember serve",
     "test": "ember try:each",
+    "test:all": "node ./scripts/run-CI-tests.js"
   },
   "dependencies": {
     "@embroider/macros": "~0.47.2",

packages/ember/scripts/run-CI-tests.js

@@ -0,0 +1,17 @@
+/*eslint-env node*/
+const { spawnSync } = require('child_process');
+
+console.log('Mimicking the CI environment in order to run tests against multiple versions of Ember');
+
+const result = spawnSync('yarn test', {
+  shell: true,
+  stdio: 'inherit',
+  env: {
+    ...process.env,
+    GITHUB_ACTIONS: true,
+    GITHUB_EVENT_NAME: 'push',
+    GITHUB_HEAD_REF: 'master',
+  },
+});
+
+process.exit(result.status);