Describe the bug
The input field for prune keep values has a two digit limit. Borg on the command line has no such limit.

To Reproduce
Steps to reproduce the behavior:

1. Go to the "Archives" tab.
2. Click on the "Prune Options and Archive Naming" subtab.
3. Click the first "Keep" field.
4. Try typing a value over 99 (this fails due to the bug).
5. Type in 99. The up arrow greys out (this shouldn't be so), making you unable to increase the value beyond 99.

Environment (please complete the following information):

• OS: Ubuntu 20.04
• Vorta version: 0.7.8
• Installed from: pip3