Update test_renderer so that tests pass with Sphinx 7.2 (#976)

Sphinx was updated in July 2023 so that importing `sphinx.testing.path`
no longer causes Sphinx application paths to belong to the 
class `sphinx.testing.path.path`, which has a `makedirs` method.

Instead, Sphinx application paths are now ordinary `Path` objects
which lack this method, so we use `os.makedirs` instead. This is
backwards compatible as `sphinx.testing.path.path` objects are
pathlike and so accepted by `os.makedirs`.

tests/test_renderer.py

@@ -35,7 +35,7 @@ def app(test_params, app_params, make_app, shared_result):
     """
     args, kwargs = app_params
     assert "srcdir" in kwargs
-    kwargs["srcdir"].makedirs(exist_ok=True)
+    os.makedirs(kwargs["srcdir"], exist_ok=True)
     (kwargs["srcdir"] / "conf.py").write_text("")
     app_ = make_app(*args, **kwargs)
     yield app_