Assign python/ sub-directory to python-codeowners (rapidsai#4940)

This ensures that all files within the python/ sub-directory have a codeowner assigned.

Special files like the python/setup.py file that is declared later will still be owned by @rapidsai/cuml-cmake-codeowners .

Authors:
  - Carl Simon Adorf (https://github.com/csadorf)

Approvers:
  - Dante Gama Dessavre (https://github.com/dantegd)
  - Sean Frye (https://github.com/sean-frye)

URL: rapidsai#4940

.github/CODEOWNERS

@@ -2,7 +2,7 @@
 cpp/               @rapidsai/cuml-cpp-codeowners
 
 #python code owners
-python/cuml/       @rapidsai/cuml-python-codeowners
+python/            @rapidsai/cuml-python-codeowners
 
 #cmake code owners
 **/CMakeLists.txt  @rapidsai/cuml-cmake-codeowners