conftest: cleanup environment cleaner (#31486)

* clean env

* no self

conftest.py

@@ -1,3 +1,4 @@
+import contextlib
 import gc
 import os
 import pytest
@@ -25,12 +26,19 @@ def pytest_runtest_call(item):
     yield
 
 
-@pytest.fixture(scope="function", autouse=True)
-def openpilot_function_fixture(request):
+@contextlib.contextmanager
+def clean_env():
   starting_env = dict(os.environ)
+  yield
+  os.environ.clear()
+  os.environ.update(starting_env)
+
 
+@pytest.fixture(scope="function", autouse=True)
+def openpilot_function_fixture(request):
   random.seed(0)
 
+  with clean_env():
     # setup a clean environment for each test
     with OpenpilotPrefix(shared_download_cache=request.node.get_closest_marker("shared_download_cache") is not None) as prefix:
       prefix = os.environ["OPENPILOT_PREFIX"]
@@ -40,9 +48,6 @@ def openpilot_function_fixture(request):
       # ensure the test doesn't change the prefix
       assert "OPENPILOT_PREFIX" in os.environ and prefix == os.environ["OPENPILOT_PREFIX"]
 
-  os.environ.clear()
-  os.environ.update(starting_env)
-
     # cleanup any started processes
     manager.manager_cleanup()
 
@@ -55,13 +60,9 @@ def openpilot_function_fixture(request):
 # so we need to hook both the function and class pytest fixtures
 @pytest.fixture(scope="class", autouse=True)
 def openpilot_class_fixture():
-  starting_env = dict(os.environ)
-
+  with clean_env():
     yield
 
-  os.environ.clear()
-  os.environ.update(starting_env)
-
 
 @pytest.fixture(scope="function")
 def tici_setup_fixture(openpilot_function_fixture):