test_tls_ext_noca fails when python3 is built againts openssl3

[mweinelt]

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Please describe the issue and your environment here.

---

Issue description:

We see test_tls_ext_noca fail when Python is built against OpenSSL 3.0.

_____________________ TestLdapCExtension.test_tls_ext_noca _____________________

self = <Tests.t_cext.TestLdapCExtension testMethod=test_tls_ext_noca>

    @requires_tls()
    def test_tls_ext_noca(self):
        l = self._open_conn(bind=False)
        l.set_option(_ldap.OPT_PROTOCOL_VERSION, _ldap.VERSION3)
        # fails because libldap defaults to secure cert validation but
        # the test CA is not installed as trust anchor.
        with self.assertRaises(_ldap.CONNECT_ERROR) as e:
            l.start_tls_s()
        # known resaons:
        # Ubuntu on Travis: '(unknown error code)'
        # OpenSSL 1.1: error:1416F086:SSL routines:\
        #    tls_process_server_certificate:certificate verify failed
        # NSS: TLS error -8172:Peer's certificate issuer has \
        #    been marked as not trusted by the user.
        msg = str(e.exception)
        candidates = ('certificate', 'tls', '(unknown error code)')
        if not any(s in msg.lower() for s in candidates):
>           self.fail(msg)
E           AssertionError: {'result': -11, 'desc': 'Connect error', 'ctrls': [], 'info': 'error:16000069:STORE routines::unregistered scheme'}

Tests/t_cext.py:916: AssertionError

Steps to reproduce:

Build Python with OpenSSL 3 and run the testsuite.

Operating system: Linux (NixOS Unstable)

Python version: 3.10.8

python-ldap version: 3.4.3