fix: use relative work tree when running from root

When running a git command from the root of the work tree, just use "." for
GIT_WORK_TREE instead of an absolute path.

This is part of a general attempt to reduce the use of absolute paths in
hopes of improving compatibility with Windows.

Author: jpgrayson

src/stupid/mod.rs

@@ -105,7 +105,7 @@ impl<'repo, 'index> StupidContext<'repo, 'index> {
         if let Some(git_dir) = self.git_dir {
             command.env("GIT_DIR", realpath(git_dir)?);
         }
-        command.env("GIT_WORK_TREE", realpath(work_dir)?);
+        command.env("GIT_WORK_TREE", ".");
         if let Some(index_path) = self.index_path {
             command.env("GIT_INDEX_FILE", realpath(index_path)?);
         }