fusepy: fix incorrect libfuse path on darwin

pkgs/development/python-modules/fusepy/default.nix

···
 { lib
+, stdenv
 , buildPythonPackage
 , fetchPypi
 , pkgs
···
   # No tests included
   doCheck = false;
 
-  patchPhase = ''
+  # On macOS, users are expected to install macFUSE. This means fusepy should
+  # be able to find libfuse in /usr/local/lib.
+  patchPhase = lib.optionalString (!stdenv.isDarwin) ''
     substituteInPlace fuse.py --replace \
       "find_library('fuse')" "'${pkgs.fuse}/lib/libfuse.so'"
   '';