[BUG] `fvm use` makes unrelated changes to settings.json.

Before creating a bug report please make check the following

• You have read our FAQ
• [n/a] If you have used flutter. Please install correctly, run pub cache repair. Close the terminal and try again.
• [n/a] If you are on Windows. Make sure you are running the terminal as administrator or with developer permissions.
• [n/a] Run fvm doctor if possible and add the output to the issue.

Describe the bug When running fvm use, the settings.json file is update to set the new version to use. However, comments are removed from the file and tabs are changed to spaces.

To Reproduce Steps to reproduce the behavior:

1. Add comments to settings.json.
2. Set it to save tabs, not spaces.
3. Run fvm use stable
4. Comments will be removed and tabs will be changed to spaces.

Expected behavior Only the version number should be changed. Tab/space indentation should match rest of file.