python3Packages.matplotlib: fix Tk

The refactor that happened in the same commit as the version bump
somehow broke Tk support.

This commit fixes the issue by moving tkinter to propagatedBuildInputs.

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

@@ -135,7 +135,6 @@ buildPythonPackage rec {
     libX11
     tcl
     tk
-    tkinter
   ] ++ lib.optionals stdenv.isDarwin [
     Cocoa
   ];
@@ -167,6 +166,8 @@ buildPythonPackage rec {
     tornado
   ] ++ lib.optionals enableNbagg [
     ipykernel
+  ] ++ lib.optionals enableTk [
+    tkinter
   ];
 
   passthru.config = {