Update net-ldap gem to latest

Open Drew Blessing requested to merge upgrade_net_ldap into master

What does this MR do?

Updates net-ldap gem to the latest (currently 0.16.0). We hope this may resolve a corner case issue seen by a customer in https://gitlab.zendesk.com/agent/tickets/80114

In quick manual testing locally, the updated gem doesn't seem to break anything. I'm going to build a package and ask the customer to test in their test environment. If all works and it solves the problem, we can ship it.