pypy3Packages.babel: fix build

babel> <frozen importlib._bootstrap>:1007:
babel> _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
babel>
babel> name = 'tzdata', import_ = <function _gcd_import at 0x00007ffff797fa00>
babel>
babel> >   ???
babel> E   ModuleNotFoundError: No module named 'tzdata'
babel>
babel> <frozen importlib._bootstrap>:984: ModuleNotFoundError
babel>
babel> During handling of the above exception, another exception occurred:

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

@@ -1,8 +1,10 @@
 { lib
 , buildPythonPackage
 , fetchPypi
+, isPyPy
 , pythonAtLeast
 , pythonOlder
+, tzdata
 
 # tests
 , freezegun
@@ -31,11 +33,12 @@ buildPythonPackage rec {
   doCheck = pythonAtLeast "3.9";
 
   nativeCheckInputs = [
-    # via setup.py
     freezegun
     pytestCheckHook
-    # via tox.ini
+    # https://github.com/python-babel/babel/issues/988#issuecomment-1521765563
     pytz
+  ] ++ lib.optionals isPyPy [
+    tzdata
   ];
 
   disabledTests = [