Rack group selection field not filtered by site

[jeremystretch]

Environment

• Python version: 3.6.9
• NetBox version: 2.9.9

Steps to Reproduce

1. Open the form to create a rack
2. Select a site
3. Select a rack group

Expected Behavior

The list of available rack groups should be limited to the selected site.

Observed Behavior

All rack groups are listed.