test: clarified assert message for test-require-json.js

PR-URL: https://github.com/nodejs/node/pull/16807
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-require-json.js

@@ -29,5 +29,6 @@ try {
 } catch (err) {
   assert.ok(
     /test[/\\]fixtures[/\\]invalid\.json: Unexpected string/.test(err.message),
-    'require() json error should include path');
+    `require() json error should include path - currently: ${err.message}`
+  );
 }