Filter out shim model class when running discoverEmberDataModels (miragejs#2569)

Author: gilest

packages/ember-cli-mirage/addon/utils/ember-data.js

@@ -11,5 +11,5 @@ export const hasEmberData =
   @hide
 */
 export function isDsModel(m) {
-  return m && typeof m.eachRelationship === 'function';
+  return m && typeof m.eachRelationship === 'function' && m.isModel === true;
 }

test-packages/01-basic-app/app/models/shim.js

@@ -0,0 +1,10 @@
+// Mimics the static apis of ShimModelClass from ember-data
+export default class Shim {
+  fields;
+  attributes;
+  relationshipsByName;
+
+  eachAttribute() {}
+  eachRelationship() {}
+  eachTransformedAttribute() {}
+}