End enrollment notification for rollout

[jaredlockhart]

A user reported they received an end enrollment notification for a rollout:

https://experimenter.services.mozilla.com/nimbus/rollout-sponsored-topsites-in-southeast-asia-and-hong-kong/summary/

We should check why that happened and fix it, so users don't mistakenly end their rollouts.

┆Issue is synchronized with this Jira Task