Fix SqlAlchemy >1.3.19 support

SQLAlchemy 1.3.19 change the excepted exception and 1.4.x
changed the enum checking behavior such that we were no
longer raising an exception matching the check.

While we had a test for this, We didn't actually
check for it anywhere in the code. And the states are
driven by the code, so the underlying test that was broken
felt redundant. As such, it has been removed.

Change-Id: I39fa3d85978555b6cb9d0884a90625b4765bac28

ironic_inspector/test/unit/test_node_cache.py

@@ -20,7 +20,6 @@ from unittest import mock
 
 import automaton
 from oslo_config import cfg
-import oslo_db
 from oslo_utils import timeutils
 from oslo_utils import uuidutils
 
@@ -1042,11 +1041,6 @@ class TestNodeInfoState(test_base.NodeStateTest):
         row = db.model_query(db.Node).get(self.node_info.uuid)
         self.assertEqual(self.node_info.state, row.state)
 
-    def test_set_invalid_state(self):
-        self.assertRaisesRegex(oslo_db.exception.DBError,
-                               'constraint failed',
-                               self.node_info._set_state, 'foo')
-
     def test_commit(self):
         current_time = timeutils.utcnow()
         self.node_info.started_at = self.node_info.finished_at = current_time