listen for SIGINT signal instead of exit key bind

**Describe the bug**
A clear and concise description of what the bug is.

**To Reproduce**
Steps to reproduce the behavior:
Remap Ctrl+Q to quit, with Ctrl+C being now available for copy/paste keybindings in terminal config:
```console
stty intr ^Q
stty -ixon
stty -ixoff
```

**Expected behavior**
Ctrl+Q should now be interpreted as SIGINT. This works for most applications, but because GitUI enables raw terminal mode, it is up to GitUI to manually respect system settings.

**Context (please complete the following information):**
- OS/Distro + Version: NixOS 23.11
- GitUI Version: gitui 0.24.3
- Rust version: unknown