bpo-34604: Fix possible mojibake in pwd.getpwnam() and grp.getgrnam() (GH-9098)

Pass the user/group name as Unicode to the formatting function,
instead of always decoding a bytes string from UTF-8.
diff --git a/Modules/grpmodule.c b/Modules/grpmodule.c
index ffdfa1b..74286ab 100644
--- a/Modules/grpmodule.c
+++ b/Modules/grpmodule.c
@@ -245,7 +245,7 @@
             PyErr_NoMemory();
         }
         else {
-            PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %s", name_chars);
+            PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %S", name);
         }
         goto out;
     }