Use the fish built-in function name to report current working directory

If the feature is enabled by fish in the future, it will override the
built-in one and there will be no duplicate reporting.

kitty_tests/shell_integration.py

@@ -171,6 +171,8 @@ function _set_status_prompt; function fish_prompt; echo -n "$pipestatus $status
             pty.send_cmd_to_child('set -q XDG_DATA_DIRS; or echo ok')
             pty.wait_till(lambda: pty.screen_contents().count(right_prompt) == 2)
             self.ae(str(pty.screen.line(1)), 'ok')
+
+            # CWD reporting
             self.assertTrue(pty.screen.last_reported_cwd.endswith(self.home_dir))
             q = os.path.join(self.home_dir, 'testing-cwd-notification-🐱')
             os.mkdir(q)