Steps to replicate the issue (include links if applicable):
Per our findings in T323050: SPIKE verify that mobile preferences toggles aren't overwriting existing checkbox handlers [8hr]

• create an onclick handler for a preference checkbox
• navigate to mobile preferences
• change the toggle for that preference

What happens?:
the onclick handler will not run

What should have happened instead?:
handlers for preferences should run

Software version (skip for WMF-hosted wikis like Wikipedia):
We had to go out of our way to create this scenario, we're not aware of this problem existing in the wild.

Other information (browser name/version, screenshots, etc.):
N/A