Fix copilot coding agent warnings

[baelter]

We currently get warning for the copilot coding agent:

Firewall rules blocked me from connecting to one or more addresses (expand for details)
I tried to connect to the following addresses, but was blocked by firewall rules:
esm.ubuntu.com
Triggering command: /usr/lib/apt/methods/https (dns block)
If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Add the suggested action configuration and report what the allowlist should look like.