fix: replace PyList_GET_ITEM()

resolves #1434

Instead use [`PyList_GetItem()`] for python < 3.13 or [`PyList_GetItemRef()`] for python >= 3.13.

Both are part of the Stable ABI but also propagate errors.
Whereas the previous [`PyList_GET_ITEM()`] did not do any error checking and was not part of the Stable ABI.

[`PyList_GetItemRef()`]: https://docs.python.org/3/c-api/list.html#c.PyList_GetItemRef
[`PyList_GetItem()`]: https://docs.python.org/3/c-api/list.html#c.PyList_GetItem
[`PyList_GET_ITEM()`]: https://docs.python.org/3/c-api/list.html#c.PyList_GET_ITEM

Author: 2bndy5

src/repository.c

@@ -599,7 +599,14 @@ merge_base_xxx(Repository *self, PyObject *args, git_merge_base_xxx_t git_merge_
     }
 
     for (; i < commit_oid_count; i++) {
-        py_commit_oid = PyList_GET_ITEM(py_commit_oids, i);
+        py_commit_oid =
+#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION < 13
+            PyList_GetItem(py_commit_oids, i);
+#else
+            PyList_GetItemRef(py_commit_oids, i);
+#endif
+        if (py_commit_oid == NULL)
+            goto out;
         err = py_oid_to_git_oid_expand(self->repo, py_commit_oid, &commit_oids[i]);
         if (err < 0)
             goto out;
@@ -1052,7 +1059,14 @@ Repository_create_commit(Repository *self, PyObject *args)
         goto out;
     }
     for (; i < parent_count; i++) {
-        py_parent = PyList_GET_ITEM(py_parents, i);
+        py_parent =
+#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION < 13
+            PyList_GetItem(py_parents, i);
+#else
+            PyList_GetItemRef(py_parents, i);
+#endif
+        if (py_parent == NULL)
+            goto out;
         len = py_oid_to_git_oid(py_parent, &oid);
         if (len == 0)
             goto out;
@@ -1135,7 +1149,14 @@ Repository_create_commit_string(Repository *self, PyObject *args)
         goto out;
     }
     for (; i < parent_count; i++) {
-        py_parent = PyList_GET_ITEM(py_parents, i);
+        py_parent =
+#if PY_MAJOR_VERSION == 3 && PY_MINOR_VERSION < 13
+            PyList_GetItem(py_parents, i);
+#else
+            PyList_GetItemRef(py_parents, i);
+#endif
+        if (py_parent == NULL)
+            goto out;
         len = py_oid_to_git_oid(py_parent, &oid);
         if (len == 0)
             goto out;