Split lookdict_unicode_nodummy() assertion to debug

Issue #27350.
diff --git a/Objects/dictobject.c b/Objects/dictobject.c
index 98515e9..cd25803 100644
--- a/Objects/dictobject.c
+++ b/Objects/dictobject.c
@@ -802,7 +802,8 @@
         return DKIX_EMPTY;
     }
     ep = &ep0[ix];
-    assert(ep->me_key != NULL && PyUnicode_CheckExact(ep->me_key));
+    assert(ep->me_key != NULL);
+    assert(PyUnicode_CheckExact(ep->me_key));
     if (ep->me_key == key ||
         (ep->me_hash == hash && unicode_eq(ep->me_key, key))) {
         if (hashpos != NULL)