[Bug] Can't delete/activate a specific grouped notification with keyboard only

**Describe the bug**
There is currently no way to delete a single notification through backspace/enter/arrow keys if they are grouped. Trying to delete it with backspace/del will delete every single notification in the grouping

**To Reproduce**
Steps to reproduce the behavior:
1. Receive multiple grouped notifications
2. Attempt to delete only one of them

**Expected behavior**
There should be a way to do this without using the mouse, as the non-grouped versions work perfectly and have good UX

**Desktop (please complete the following information):**
- OS: Mint w/ sway
- Version: latest git revision as of today

No files, tests, or code entry points are named. Reproduce the issue with multiple grouped notifications on Mint under sway using the latest git revision, then trace the keyboard handling for grouped notifications; done means one grouped notification can be activated or deleted without affecting the others.

Written by the indexing model from the issue text.