[DRE-maint] ruby-net-ssh-gateway is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-net-ssh-gateway 2.0.0-1 is marked for autoremoval from testing on 2020-04-07

It (build-)depends on packages with these RC bugs:
952086: ruby-highline: FTBFS: ERROR: Test "ruby2.7" failed: Error: test_Highline_String_is_yaml_serializable(TestStringExtension): RuntimeError: CRITICAL: RUBYGEMS_ACTIVATION_MONITOR.owned?: before false -> after true