Start using xdist in pytest opts

We have `pytest-xdist` already installed, but we aren't using it.

Set `-n auto --maxprocesses 8` in our config, so that it will be
activated. The max prevents `-n auto` from starting large numbers of
workers (e.g., 20) and losing any speed benefit to overheads. Using
`-n auto` rather than (e.g., `-n 4`) ensures that in CI and other
variable environments, we get the right number of workers.

One test with a randomized parameter needed a tweak, as it made an
xdist parameter consistency check fail.

pyproject.toml

@@ -75,7 +75,7 @@ attr = "globus_cli.version.__version__"
 profile = "black"
 
 [tool.pytest.ini_options]
-addopts = "--timeout 3 --color=yes"
+addopts = "-n auto --maxprocesses 8 --timeout 3 --color=yes"
 filterwarnings = ["error"]
 
 [tool.scriv]

tests/functional/gcs/endpoint/test_set_subscription_id.py

@@ -5,7 +5,9 @@
 from globus_sdk._testing import load_response_set
 
 
-@pytest.mark.parametrize("subscription_id", (str(uuid.uuid4()), "DEFAULT", "null"))
+@pytest.mark.parametrize(
+    "subscription_id", (str(uuid.UUID(int=101)), "DEFAULT", "null")
+)
 def test_gcs_endpoint_set_subscription_id(subscription_id, run_line, add_gcs_login):
     meta = load_response_set("cli.collection_operations").metadata
     endpoint_id = meta["endpoint_id"]