Safer use of Object.prototype.hasOwnProperty (#3069)

* Safer use of `Object.prototype.hasOwnProperty`

Fixes an error I get when GraphQL JS passes a prototypeless object into the resolver

```
ReferenceError: maybeRef is not defined
    at eval (eval at <anonymous> (/Users/mattalexander/Projects/edge-sites-schema/tests/regression.test.js:67:7), <anonymous>:1:38)
    at forEach (/projectpath/tests/regression.test.js:67:7)
    at Array.forEach (<anonymous>)
    at Object.<anonymous> (/projectpath/tests/regression.test.js:65:17)
```

* changeset and test

Co-authored-by: Arda TANRIKULU <ardatanrikulu@gmail.com>

.changeset/fifty-wombats-help.md

@@ -0,0 +1,5 @@
+---
+'@graphql-tools/mock': patch
+---
+
+Safer use of Object.prototype.hasOwnProperty #3069

packages/mock/src/types.ts

@@ -190,7 +190,7 @@ export type Ref<KeyT extends KeyTypeConstraints = string> = {
 };
 
 export function isRef<KeyT extends KeyTypeConstraints = string>(maybeRef: unknown): maybeRef is Ref<KeyT> {
-  return maybeRef && typeof maybeRef === 'object' && maybeRef.hasOwnProperty('$ref');
+  return maybeRef && typeof maybeRef === 'object' && '$ref' in maybeRef;
 }
 
 export function assertIsRef<KeyT extends KeyTypeConstraints = string>(