maintainers: create sage team

Maintaining all the packages whose updates might break some aspect of
sage.

For reference:
https://github.com/NixOS/nixpkgs/pull/103810#issuecomment-727536510

pkgs/applications/science/math/pari/default.nix

@@ -74,7 +74,7 @@ stdenv.mkDerivation rec {
     homepage = "http://pari.math.u-bordeaux.fr";
     downloadPage = "http://pari.math.u-bordeaux.fr/download.html";
     license = licenses.gpl2Plus;
-    maintainers = with maintainers; [ ertes raskin AndersonTorres timokau ];
+    maintainers = with maintainers; [ ertes raskin AndersonTorres ] ++ teams.sage.members;
     platforms = platforms.linux ++ platforms.darwin;
     updateWalker = true;
   };