Close custom object stream in regression test

The Python package test (windows, 3.7) check failed during TemporaryDirectory cleanup because the GitDB regression left its loose-object mmap open, producing WinError 5 while deleting the object file.

Close the object stream explicitly and use Repo's context manager so Windows releases both resources before temporary-directory cleanup.

Validation: focused regression test; Ruff check and format; mypy; compileall; git diff --check.

Author: codex

test/test_repo.py

@@ -247,9 +247,14 @@ def test_repo_discovery_preserves_object_directory(self):
             with cwd(tdir), mock.patch.dict(os.environ, {"GIT_DIR": "git", "GIT_OBJECT_DIRECTORY": "objects"}):
                 repo = Repo(odbt=GitDB)
 
-            assert osp.samefile(repo.odb.root_path(), object_dir)
-            assert repo.odb.stream(bytes.fromhex(blob_hexsha)).read() == payload
-            assert repo.git.cat_file("blob", blob_hexsha) == payload.decode()
+            with repo:
+                assert osp.samefile(repo.odb.root_path(), object_dir)
+                object_stream = repo.odb.stream(bytes.fromhex(blob_hexsha))
+                try:
+                    assert object_stream.read() == payload
+                finally:
+                    object_stream.stream.close()
+                assert repo.git.cat_file("blob", blob_hexsha) == payload.decode()
 
     @with_rw_repo("0.3.2.1")
     def test_repo_creation_from_different_paths(self, rw_repo):