Impossible to change capitalization of the tags

### Expected
Tags can be renamed, unless the new name contains forbidden characters.

### Observed
It's impossible to change a capitalization of a letter in a tag. E.g. `country` can't be renamed to `Country`:

https://user-images.githubusercontent.com/73365754/130058761-cd31613e-abca-40c4-9b1e-7eb1fdc7912f.MP4

### 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 ~> this is not possible.

Make|Model|iOS Version|App Version
-|-|-|-
iPhone|XR|14.7.1|4.42.0.0

Start by reproducing the tag rename flow in Settings using the country-to-Country example on an iPhone or iOS simulator. Trace the tag-editing entry point and verify that changing only capitalization is accepted while forbidden characters remain rejected; done means the renamed tag appears with the requested casing.

Written by the indexing model from the issue text.