Fix custom Brave Ad notifications should not disappear after minimizing and restoring the browser

[btlechowski]

Follow up to #19464.
custom ad notification disappears when attached to Brave Window after minimizing and restoring the browser

Steps to Reproduce

1. Clean install
2. Run Brave with: --enable-logging=stderr --vmodule="*/variations/*"=6,"*/bat-native-ledger/*"=6,"*/brave_rewards/*"=6,"*/bat-native-ads/*"=6,"*/bat-native-confirmations/*"=6,"*/brave_ads/*"=9,"*/brave_user_model/*"=6,"*/bat_ads/*"=6 --brave-ads-staging --rewards=staging=true --variations-server-url=https://v --enable-features="CustomAdNotifications:should_attached_ad_notification_to_browser_window/true"
3. Enable rewards and ads
4. Trigger a notification ad
5. Minimize the browser
6. Restore the browser

Actual result:

custom ad notification disappears
There is no logs registered

Expected result:

custom ad notification re-appears with the browser window

Reproduces how often:

Easily reproduced

Brave version (brave://version info)

Brave	1.38.83 Chromium: 100.0.4896.79 (Official Build) beta (64-bit)
Revision	8fb749dcab8700c24213791969e59deb72fee36f-refs/branch-heads/4896@{#1015}
OS	Ubuntu 18.04 LTS

cc @brave/qa-team @jsecretan @tmancey @aseren

[tmancey]

Closed as resolved by #22203