test: add TODO for a test case that hangs at the moment

Author: ayberkt

examples/test_sat_solver.py

@@ -189,3 +189,7 @@ def test_example_prime121() -> None:
     is_sat: bool = check_sat_file("prime121")
     assert(is_sat)
 
+# TODO: the following hangs.
+def test_example_prime289() -> None:
+    is_sat: bool = check_sat_file("prime289")
+    assert(is_sat)