Update net-ldap gem version

What does this MR do?

Related issue: #257438 (closed)

Updates net-ldap gem: https://github.com/ruby-ldap/ruby-net-ldap to 0.16.3

It eliminates some Ruby 2.7 kwargs warnings and provides multiple useful improvements

History: https://github.com/ruby-ldap/ruby-net-ldap/blob/master/History.rdoc

Diff: https://github.com/ruby-ldap/ruby-net-ldap/compare/v0.16.2..v0.16.3

There's 0.17.0 version already available, but it removes ConnectionRefusedError which exists in our code. Since 0.16.3 still removes the 2.7 warning, let's go the safer way 👍