Make test_external_ca.py compatible with crypto 41.0.0
    
    The integration test test_external_ca.py is not compatible with
    python-cryptography 41.0.0+.
    
    The test is installing ipa server with an externally-signed CA cert
    using a Microsoft Certificate Service profile:
    ipa-server-install --external-ca --external-ca-type ms-cs
                        --external-ca-profile "1.2.3.4:10:200"
    The command generates a CSR in /root/ipa.csr. The test reads the CSR,
    extracts the extensions and compares with the requested extension
    for the Microsoft Template.
    With python-cryptography 41.0.0+, the extension can be decoded as
    cryptography.x509.MSCertificateTemplate while with older version
    the extension is decoded as cryptography.x509.UnrecognizedExtension.
    
    Handle both cases properly.
    
    Fixes: https://pagure.io/freeipa/issue/9490
    
    Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
    Reviewed-By: Michal Polovka <mpolovka@redhat.com>