Fix NULL test in _testinternalcapi (GH-92861)

(cherry picked from commit 702e0da000bf28aa20cb7f3893b575d977506495)

Co-authored-by: Dennis Sweeney <36520290+sweeneyde@users.noreply.github.com>

Modules/_testinternalcapi.c

diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 914b20b..238de74 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -307,7 +307,7 @@ check_edit_cost(const char *a, const char *b, Py_ssize_t expected)
         goto exit;
     }
     b_obj = PyUnicode_FromString(b);
-    if (a_obj == NULL) {
+    if (b_obj == NULL) {
         goto exit;
     }
     Py_ssize_t result = _Py_UTF8_Edit_Cost(a_obj, b_obj, -1);