Add CODEOWNERS entry for pathlib (GH-32202)

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 33a3ebb..62ee6f8 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -146,3 +146,6 @@
 # macOS
 /Mac/                         @python/macos-team
 **/*osx_support*              @python/macos-team
+
+# pathlib
+**/*pathlib*                  @brettcannon