DOC Update broken link in conftest.py (scikit-learn#19736)

conftest.py

@@ -1,7 +1,7 @@
 # Even if empty this file is useful so that when running from the root folder
 # ./sklearn is added to sys.path by pytest. See
-# https://docs.pytest.org/en/latest/pythonpath.html for more details.  For
-# example, this allows to build extensions in place and run pytest
+# https://docs.pytest.org/en/latest/explanation/pythonpath.html for more
+# details. For example, this allows to build extensions in place and run pytest
 # doc/modules/clustering.rst and use sklearn from the local folder rather than
 # the one from site-packages.