odb backend: pass the object type to write_cb as an int

The type was passed to PyObject_CallMethod with the "n" format, which
reads a Py_ssize_t, but git_object_t is an int. On 64-bit Windows
write_cb received garbage in the upper 32 bits, e.g. 2753074036739
(0x28100000003) instead of 3 for a blob.

Assisted-by: Claude Fable 5.1

Author: cboos

src/odb_backend.c

@@ -189,7 +189,7 @@ pgit_odb_backend_write(git_odb_backend *_be, const git_oid *oid,
     if (py_oid == NULL)
         goto done;
 
-    result = PyObject_CallMethod(be->py_backend, "write_cb", "Ny#n", py_oid, data, sz, typ);
+    result = PyObject_CallMethod(be->py_backend, "write_cb", "Ny#i", py_oid, data, sz, (int)typ);
     if (result == NULL) {
         err = git_error_for_exc();
         goto done;

test/test_odb_backend.py

@@ -334,3 +334,25 @@ def test_index_add(testrepo: Repository) -> None:
     subprocess.run(
         [sys.executable, '-c', INDEX_ADD_SCRIPT, testrepo.workdir], check=True
     )
+
+
+class WriteBackend(pygit2.OdbBackend):
+    def __init__(self) -> None:
+        super().__init__()
+        self.written: list[tuple[Oid, bytes, int]] = []
+
+    def exists_cb(self, oid: Oid | str) -> bool:
+        return False
+
+    def refresh_cb(self) -> None:
+        pass
+
+    def write_cb(self, oid: Oid, data: bytes, typ: int) -> None:
+        self.written.append((oid, data, typ))
+
+
+def test_write_cb(testrepo: Repository) -> None:
+    backend = WriteBackend()
+    testrepo.odb.add_backend(backend, 100)
+    oid = testrepo.create_blob(b'hello')
+    assert backend.written == [(oid, b'hello', ObjectType.BLOB)]