test(Session.attach): Remove xfail now that bug is fixed

why: The fix in the previous commit resolves the issue, so the test
should now pass and serve as a permanent regression guard.
what:
- Remove xfail marker from test_session_attach_does_not_fail_if_session_killed_during_attach

Author: tony

tests/test_session.py

@@ -515,12 +515,6 @@ class SessionAttachRefreshFixture(t.NamedTuple):
 ]
 
 
-@pytest.mark.xfail(
-    reason="Bug: attach() calls refresh() which fails if session killed during attach. "
-    "See: https://github.com/tmux-python/tmuxp/issues/1002",
-    raises=Exception,
-    strict=True,
-)
 @pytest.mark.parametrize(
     list(SessionAttachRefreshFixture._fields),
     SESSION_ATTACH_REFRESH_FIXTURES,