Test TestSSHUserConfig.test_missing_hostkey fails with paramiko < 3.2

[0EVSG]

Describe the bug

When running the tests with paramiko < 3.2 installed, the test TestSSHUserConfig.test_missing_hostkey fails due to missing PKey method from_type_string:

__________________________________ TestSSHUserConfig.test_missing_hostkey ___________________________________

self = <tests.test_connectors.test_sshuserclient.TestSSHUserConfig testMethod=test_missing_hostkey>

    def test_missing_hostkey(self):
        client = SSHClient()
        policy = AskPolicy()
        example_hostname = "new_host"
        example_keytype = "ecdsa-sha2-nistp256"
        example_key = (
            "AAAAE2VjZHNhLXNoYTItbmlzdHAyNT"
            "YAAAAIbmlzdHAyNTYAAABBBHNp1NM"
            "ZjxPBuuKwIPfkVJqWaH3oUtW137kIW"
            "P4PlCyACt8zVIIimFhIpwRUidcf7jw"
            "VWPAJvfBjEPqewDApnZQ="
        )

>       key = PKey.from_type_string(
            example_keytype,
            b64decode(example_key),
        )
E       AttributeError: type object 'PKey' has no attribute 'from_type_string'

tests/test_connectors/test_sshuserclient.py:241: AttributeError

According to paramiko docs this method was only added in paramiko 3.2, but the required paramiko version is >= 2.7 in setup.py.

To Reproduce

I stumbled upon this while trying to update the FreeBSD port, where paramiko is at version 2.11 currently. The failing test should be reproducible in any environment with paramiko < 3.2 though.