tests: use is None for comparision against None

Fix ruff lint E711.

Signed-off-by: Jeremy Kerr <jk@codeconstruct.com.au>

Author: jk-ozlabs

tests/test_mctp.py

@@ -43,7 +43,7 @@ async def test_route_add_single_direct(mctp):
     assert len(mctp.system.routes) == 1
     route = mctp.system.routes[0]
     assert route.iface.name == "mctp0"
-    assert route.gw == None
+    assert route.gw is None
     assert route.start_eid == 9
     assert route.end_eid == 9
     assert route.mtu == 0
@@ -54,7 +54,7 @@ async def test_route_add_single_gw(mctp):
 
     assert len(mctp.system.routes) == 1
     route = mctp.system.routes[0]
-    assert route.iface == None
+    assert route.iface is None
     assert route.gw[0] == 1
     assert route.gw[1] == 9
     assert route.start_eid == 10