Ignoring .gitignore just keeps adding .gitignore in .gitignore

[ignatenkobrain]

Describe the bug

I think subject covers it pretty well.

To Reproduce
Steps to reproduce the behavior:

1. Make sure your repository does not have any .gitignore in it
2. Ignore any file (so that .gitignore would be created by gitui)
3. Try to ignore .gitignore
4. The .gitignore is added to the .gitignore (and if you repeat, it is added infinitely)

Expected behavior

Either ignoring .gitignore would not do anything or throw an error.

Screenshots

Context (please complete the following information):

• OS/Distro + Version: Fedora 35
• GitUI Version: 0.16.2
• Rust version: 1.53

Additional context

None.

[extrawurst]