Fix tests on Python < 3.11

Author: srittau

test_asserts.py

@@ -1516,7 +1516,7 @@ def test_assert_json_subset__presence_check(self) -> None:
             assert_json_subset({"foo": Absent()}, {"foo": "bar"})
 
     def test_assert_json_subset__existence_check_old(self) -> None:
-        with catch_warnings(category=DeprecationWarning):
+        with catch_warnings():
             simplefilter("ignore")
             with assert_succeeds(AssertionError):
                 assert_json_subset({Exists("foo"): True}, {"foo": "bar"})