Restrict egress traffic in CI/CD

Restrict egress traffic from the build system to authorized destinations. This is pretty straightforward and a very feasible mitigation since a build system usually requires access to a very limited destinations.
Controlling the traffic has many benefits:
1. Prevent exfiltration of sensitive information
2. Block download of packages from unauthorized package repositories
3. Block download of malware

Applies to

T0147 Scan public CI/CD configurations for secrets and vulnerable actions
T0120 Dependency confusion

References

https://about.codecov.io/security-update/