fix a bug for XML results parsing.

[bukun]

found this bug when requesting DistributedSearch via pycsw with federatedcatalogues config. Just as follows:

    File "/home/bk/vpy_csw/lib/python3.9/site-packages/owslib/catalogue/csw3.py", line 225, in getrecords
        if xml.startswith(b'<'):
    TypeError: startswith first arg must be str or a tuple of str, not bytes