testing: fix an assert

The assert as written was always true, according to the name `failures`
it intended the first element of the tuple.

testing/test_looponfail.py

@@ -122,7 +122,7 @@ class TestRemoteControl:
         item = pytester.getitem("def test_func():\n assert 0\n")
         control = RemoteControl(item.config)
         control.setup()
-        failures = control.runsession()
+        failures = control.runsession()[0]
         assert failures
         control.setup()
         item.path.write_text("def test_func():\n assert 1\n")