fix invalid condition in compLabeledSys in unittest

[robinzyb]

"virials" not in self.system_1

always returns True.

Quick check by inserting and run unittest:

        #     self.assertEqual(len(self.system_1['virials']), 0)
        #     return
        print("valid condition:", not self.system_1.has_virial())
        print("current condition:", "virials" not in self.system_1)
        if not self.system_1.has_virial():
            self.assertFalse(self.system_2.has_virial())
            return
        np.testing.assert_almost_equal(
            self.system_1["virials"],

[robinzyb]

Failed tests should be carefully examed. Please contact corresponding maintainers.

[njzjz]

I fix the tests in #604