Integrate pytest-randomly into the test suite

As a lot of the integration tests populate the database with test data,
it is deemed safer to run the tests in random order to uncover potential
dependencies between distinct test cases.
Because of how the `db_session` fixture is designed, this should already
be taken care of.

noxfile.py

@@ -226,6 +226,7 @@ def test(session):
         'pytest',
         'pytest-cov',
         'pytest-env',
+        'pytest-randomly',
         'xdoctest[optional]',
     )
 
@@ -240,6 +241,7 @@ def test(session):
         '--cov-branch',
         '--cov-fail-under=100',
         '--cov-report=term-missing:skip-covered',
+        '--randomly-seed=4287',
         '-k',
         'not e2e',
         PYTEST_LOCATION,