test: fix mock of tempfile.TemporaryDirectory

Since we use this as a context manager we need to go "deeper" to set the return
value on the correct attribute. The previous version fails on Python 3.13 as
Path objects can no longer be used as context managers.

tests/unit/test_oci.py

@@ -42,52 +42,52 @@
 }
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_run(mocker):
     return mocker.patch("rockcraft.oci._process_run")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_archive_layer(mocker):
     return mocker.patch("rockcraft.layers.archive_layer")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_rmtree(mocker):
     return mocker.patch("shutil.rmtree")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_mkdir(mocker):
     return mocker.patch("pathlib.Path.mkdir")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_mkdtemp(mocker):
     return mocker.patch("tempfile.mkdtemp")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_tmpdir(mocker):
     return mocker.patch("tempfile.TemporaryDirectory")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_inject_variant(mocker):
     return mocker.patch("rockcraft.oci._inject_architecture_variant")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_read_bytes(mocker):
     return mocker.patch("pathlib.Path.read_bytes")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_write_bytes(mocker):
     return mocker.patch("pathlib.Path.write_bytes")
 
 
-@pytest.fixture()
+@pytest.fixture
 def mock_add_layer(mocker):
     return mocker.patch("rockcraft.oci.Image.add_layer")
 
@@ -313,7 +313,7 @@ def test_add_new_user(
         tmp_path,
     ):
         fake_tmpfs = tmp_path / "mock-tmp"
-        mock_tmpdir.return_value = fake_tmpfs
+        mock_tmpdir.return_value.__enter__.return_value = str(fake_tmpfs)
 
         image = oci.Image("a:b", Path("/c"))
         image.add_user(
@@ -457,7 +457,7 @@ def test_append_new_user(
                 (fake_prime_etc / f".wh.{filename}").touch()
 
         fake_tmp_new_layer = tmp_path / "mock-tmp"
-        mock_tmpdir.return_value = fake_tmp_new_layer
+        mock_tmpdir.return_value.__enter__.return_value = str(fake_tmp_new_layer)
 
         image = oci.Image("a:b", Path("/c"))
         image.add_user(
@@ -746,7 +746,7 @@ def test_set_pebble_layer(
         mock_define_pebble_layer.return_value = None
 
         fake_tmpfs = tmp_path / "mock-tmp-pebble-layer-path"
-        mock_tmpdir.return_value = fake_tmpfs
+        mock_tmpdir.return_value.__enter__.return_value = str(fake_tmpfs)
 
         image.set_pebble_layer(
             mock_services,