Update Setuptools URL

Co-authored-by: Stan Ulbrych <[email protected]>

Author: encukou

Doc/extending/building.rst

@@ -24,7 +24,7 @@ Building C and C++ Extensions with setuptools
 Building, packaging and distributing extension modules is best done with
 third-party tools, and is out of scope of this document.
 One suitable tool is Setuptools, whose documentation can be found at
-https://setuptools.readthedocs.io/en/latest/setuptools.html.
+https://setuptools.pypa.io/en/latest/setuptools.html.
 
 The :mod:`distutils` module, which was included in the standard library
 until Python 3.12, is now maintained as part of Setuptools.