Fix SSH tunnel for SSH servers with certain configuration (#18591)

Version 2.6.0 until 2.7.0 of org.apache.sshd has a bug that
will fail to connect to SSH servers configured to use
`-oKexAlgorithms=diffie-hellman-group-exchange-sha256`.

Reverting to the known working version. We can upgrade
to 2.7.1 once it is released.

Reference: https://issues.apache.org/jira/browse/SSHD-1163

Fixes #18316