bpo-32604: Fix memory leaks in the new _xxsubinterpreters module. (GH-5507)

(cherry picked from commit 4e9da0d163731caa79811c723c703ee416c31826)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>
diff --git a/Python/pystate.c b/Python/pystate.c
index a474549..8dbda73 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -1242,6 +1242,7 @@
             break;
         }
     }
+    Py_DECREF(cls);
     PyThread_release_lock(_PyRuntime.xidregistry.mutex);
     return getdata;
 }