Reconsider nokogiri gem lock for opennebula and opennebula-cli rubygems

[xorel]

In https://github.com/OpenNebula/one-ee/pull/2995 we introduced gem lock for nokogiri <1.16.

We agreed in OpenNebula we should reconsider this and either revert or require ruby >= 3.0 (same as nokogiri does).