requirements: Workaround pylibssh Failed to open session

Workaround ansible pylibssh issue which causes test failures

   pylibsshext.errors.LibsshChannelException: Failed to open_session: [-2]

PR ansible/pylibssh#756 is under review
but workaround it in the meantime.

Author: justin-stephenson

src/tests/system/requirements.txt

@@ -1,5 +1,7 @@
 flaky
 pytest
+# Workaround SSH_AGAIN and install from https://github.com/ansible/pylibssh/pull/756
+ansible-pylibssh@git+https://github.com/justin-stephenson/pylibssh@51b9a9b1811b4befafcd0a859e48dcc2822a253c
 git+https://github.com/next-actions/pytest-importance
 git+https://github.com/next-actions/pytest-mh
 git+https://github.com/next-actions/pytest-ticket