ci: skip `LICENSE.txt` copy for Ent releases

[zalimeni]

Follow-up to https://github.com/hashicorp/consul/pull/21035 to avoid unintentional side-effects when run outside of CE repo.

• Ensure we do not unintentionally copy CE LICENSE.txt to Ent release artifacts.
• Rework Go Build jobs to avoid future sync conflicts by handling CE and Ent builds simultaneously.

Tested here: https://github.com/hashicorp/consul/actions/runs/8974943569