Switched to using pytest_sessionstart instead of an autouse fixture

tests/conftest.py

@@ -4,19 +4,14 @@
 import torch.backends.mps
 
 
-@pytest.fixture(scope="session", autouse=True)
-def set_backend():
-    os.environ["KERAS_BACKEND"] = "torch"
-    yield
-
-
-@pytest.fixture(scope="session", autouse=True)
-def set_device_arm_macos_ci():
+def pytest_sessionstart(session):
     """
     Ensure that the device is set to CPU when running on arm based macOS
     GitHub runners. This is to avoid the following error:
     https://discuss.pytorch.org/t/mps-back-end-out-of-memory-on-github-action/189773/5
     """
+    os.environ["KERAS_BACKEND"] = "torch"
+
     if (
         os.getenv("GITHUB_ACTIONS") == "true"
         and torch.backends.mps.is_available()
@@ -26,5 +21,3 @@ def set_device_arm_macos_ci():
         keras.src.backend.common.global_state.set_global_attribute(
             "torch_device", "cpu"
         )
-
-        yield