Revert change to require_git(false) in WalkBuilder (#6368)

## Summary

This was changed to fix https://github.com/astral-sh/ruff/issues/5930
(respect `.gitignore` for unzipped source repositories), but led to
undesirable behavior whereby `.gitignore` files in parent directories
are respected regardless of whether you're working in a child git
repository (see: https://github.com/astral-sh/ruff/issues/6335). The
latter is a bigger problem than the former is an important use-case to
support, so pragmatically erring on the side of a revert.

Closes https://github.com/astral-sh/ruff/issues/6335.

crates/ruff/src/resolver.rs

@@ -262,7 +262,6 @@ pub fn python_files_in_path(
         builder.add(path);
     }
     builder.standard_filters(pyproject_config.settings.lib.respect_gitignore);
-    builder.require_git(false);
     builder.hidden(false);
     let walker = builder.build_parallel();