Replace deprecated makeSuite with loadTestsFromTestCase

[franzpoeschel]

Removed with Python 3.13
Relevant for 0.16 releases due to #1675

def makeSuite(testCaseClass, prefix='test', sortUsing=util.three_way_cmp,
              suiteClass=suite.TestSuite):
    import warnings
    warnings.warn(
        "unittest.makeSuite() is deprecated and will be removed in Python 3.13. "
        "Please use unittest.TestLoader.loadTestsFromTestCase() instead.",
        DeprecationWarning, stacklevel=2
    )
    return _makeLoader(prefix, sortUsing, suiteClass).loadTestsFromTestCase(
        testCaseClass)