[ads] Back/forward page transitions should not trigger `NotifyTab[Text/Html]ContentDidChange`

[aseren]

Steps to Reproduce

1. Do a search query on search.brave.com
2. Tap any link with URL other then brave.com
3. Tap Back button
4. Tap Forward button

Actual result:

Back/Forward transition doesn't trigger NotifyTab[Text/Html]ContentDidChange

Expected result:

Back/Forward transition triggers NotifyTab[Text/Html]ContentDidChange

Reproduces how often: [Easily reproduced, Intermittent Issue]

Easily reproduced