Is there a public example certificate with an expiry date above 2050 which I could fetch in order to test a script?

I would use

    conn = ssl.create_default_context().wrap_socket(socket.socket(socket.AF_INET), server_hostname=hostname) 
    conn.connect((hostname, 443))
    cert = conn.getpeercert()
    print(cert['notAfter'])

to test it.