enforce the right type for since and until in frontmatter

content/ember-data/v5/ember-data-deprecate-store-extends-ember-object.md

@@ -1,7 +1,7 @@
 ---
 title: Store will no longer extend EmberObject in 6.0
-until: 6.0
-since: 5.4
+until: '6.0'
+since: '5.4'
 displayId: ember-data:deprecate-store-extends-ember-object
 ---
 
@@ -28,4 +28,4 @@ If you are unsure whether your Store class uses EmberObject APIs, set this
 config and uses of those APIs will throw exceptions. The most common API that 
 may have been used is `Store.extend({...`.
 
-This deprecation is from RFC [#1026](https://rfcs.emberjs.com/id/1026-ember-data-deprecate-store-extends-ember-object).
+This deprecation is from RFC [#1026](https://rfcs.emberjs.com/id/1026-ember-data-deprecate-store-extends-ember-object).

node-tests/index.mjs

@@ -24,6 +24,16 @@ describe('Json Tests', function () {
           `You don't need to define a displayId if it's the same as the file name`
         );
       }
+
+      // since is manditory and must be a string
+      if (typeof contents.since !== 'string') {
+        throw new Error('since frontmatter must be a string');
+      }
+
+      // if you define an until then it must be a string
+      if (contents.until && typeof contents.until !== 'string') {
+        throw new Error('until frontmatter must be a string');
+      }
     });
   });
 });