Don't show "New notifications" bubble when "Only mentions" is selected and notification type is not a mention

**Describe the bug**
A clear and concise description of what the bug is.
- Which site: phanpy.social
- Which instance: all

**To Reproduce**
Steps to reproduce the behavior:
1. Show 'Notifications' column
2. Click on 'Only mentions' filter
3. Wait for like, boost, etc. of your toots
4. "New notifications" is shown

**Expected behavior**
"New notifications" should only be shown for mentions.

Reproduce the issue on phanpy.social by showing a Notifications column, selecting Only mentions, and waiting for a like or boost. Trace the condition that displays the New notifications bubble; done means non-mention notifications do not display it while mention notifications still do.

Written by the indexing model from the issue text.