Fix jquery-integration optional feature flag to only throw when explicitly enabled.

(cherry picked from commit 52413c2)

Author: simonihmig

lib/index.js

@@ -63,7 +63,6 @@ module.exports = {
   name: 'ember-source',
   paths,
   absolutePaths,
-  _jqueryIntegrationEnabled: true,
   _overrideTree: undefined,
 
   included() {
@@ -143,10 +142,12 @@ module.exports = {
       }
     }
 
-    this._jqueryIntegrationEnabled =
-      !optionalFeaturesMissing && optionalFeatures.isFeatureEnabled('jquery-integration');
-
-    if (this._jqueryIntegrationEnabled) {
+    if (
+      !optionalFeaturesMissing &&
+      optionalFeatures.isFeatureEnabled('jquery-integration') &&
+      typeof optionalFeatures.isFeatureExplicitlySet === 'function' &&
+      optionalFeatures.isFeatureExplicitlySet('jquery-integration')
+    ) {
       const SilentError = require('silent-error');
       throw new SilentError(
         'Setting the `jquery-integration` optional feature flag to `true` was deprecated in Ember 3.x and removed in Ember 4.0.0. You must add the `@ember/optional-features` addon and set this feature to `false`.\n\nFor more information, see the deprecation guide: https://deprecations.emberjs.com/v3.x/#toc_optional-feature-jquery-integration'