Add release-assets.githubusercontent.com to egress allowlist

Cosign installer downloads from this domain. Without it the
compile workflow fails at the Install cosign step.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ltagliaferri

.github/workflows/compile-ai-docs-from-gcs.yaml

@@ -55,6 +55,7 @@ jobs:
           objects.githubusercontent.com:443
           pypi.org:443
           raw.githubusercontent.com:443
+          release-assets.githubusercontent.com:443
           rekor.sigstore.dev:443
           run.googleapis.com:443
           sts.googleapis.com:443