[`flake8-pathlib`] Fix `--select` for `os-path-dirname` (`PTH120`) (#15446)

## Summary

Closes https://github.com/astral-sh/ruff/issues/15439.

crates/ruff_linter/src/checkers/ast/analyze/expression.rs

@@ -974,6 +974,7 @@ pub(crate) fn expression(expr: &Expr, checker: &mut Checker) {
                 Rule::OsPathIsabs,
                 Rule::OsPathJoin,
                 Rule::OsPathBasename,
+                Rule::OsPathDirname,
                 Rule::OsPathSamefile,
                 Rule::OsPathSplitext,
                 Rule::BuiltinOpen,