ci: run integration tests serially

Integration tests are incredibly flakey currently. Perhaps this is
related to the parallel execution of the tests. Certainly the fact that
the tests are randomly distributed across threads doesn't help with
figuring out what works and what doesn't.

Author: james-garner-canonical

tox.ini

@@ -63,7 +63,7 @@ envdir = {toxworkdir}/py3
 commands =
     pip install urllib3<2
     pip install pylxd
-    python -m pytest --tb native -ra -v -n auto -k 'integration' -m 'not serial' {posargs}
+    python -m pytest --tb native -ra -v -n 1 -k 'integration' -m 'not serial' {posargs}
 
 [testenv:unit]
 envdir = {toxworkdir}/py3