allow `uv lock` to fail when lock file is "corrupted"

I recently switched to using `0.5.6` and when I do a rebase and run `uv lock` to update it, it now fails with the error

```
error: Failed to parse `uv.lock`
  Caused by: TOML parse error at line 1356, column 1
     |
1356 | <<<<<<< Updated upstream
     | ^
invalid key
```

Which didn't happen before (I don't have the version in mind, sorry)

Could we get that back ?