The change of letters casing in tags is not reflected in notes

[A somewhat similar issue in iOS.](https://github.com/Automattic/simplenote-ios/issues/1402#issue-974550239)

### Expected
If the tag was renamed from `country` to `Country`, this tag should look like `Country` inside the notes.

### Observed
It remains `country` inside the notes:

https://user-images.githubusercontent.com/73365754/130059913-12ef71d6-f04c-4257-b6fb-eb73760aed6f.mov

### Reproduced
1. Open a note
2. Add a new tag to the note
3. Open Settings
4. Change the casing of any letter in this tag ~> the tag will be renamed in the Sidebar, but still remain with previous casing in inside the notes.

### Where did you see the bug
- OS: Windows 10 Home in Parallels Desktop on macOS 11.2.3
- Simplenote app version: 2.17.0-beta1

Reproduce the issue in the Simplenote desktop app using the listed steps, then trace how tag renames update the Sidebar and the tags displayed inside notes. Done means changing a tag from `country` to `Country` updates its casing consistently inside the note as well as in the Sidebar.

Written by the indexing model from the issue text.