snapcraft pack failure from git worktree

Testing with snapcraft version 7.5.0 (build 9510), building a project checked out using a git worktree fails.

Example:

initialize a project with `snapcraft init`
add to the part {source:., source-type: git}

```
parts:
  my-part:
    plugin: nil
    source: .
    source-type: git
```

commit this to a git repo
use `git worktree add` to create a worktree
change to the worktree directory
attempt to `snapcraft pack`