tests: Mark failing corner case tests as expected for 2.6.0

These are still important problems, but it will allow us to fully
leverage CI while waiting for the fixes.

test/project.t

@@ -454,6 +454,7 @@ class TestBug1430(TestCase):
         self.assertEqual("home/garden\n", out)
 
 
+@unittest.expectedFailure
 class TestBug1617(TestCase):
     def setUp(self):
         """Executed before each test in the class"""