AGENTS.md: skip archived repositories when working on pull requests across repositories (#179)

Open Dependabot pull requests of archived repositories (e.g. docker-radicale, docker-socat) were reported as still to do, with access requests suggested for them, although archived repositories are read-only.

Source: https://github.com/fphammerle/docker-postfix/blob/254700518ad841d53e28b75d651986ee6fc3b56c/AGENTS.md (fphammerle/docker-postfix#161)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -74,6 +74,9 @@
 - Pull requests / branches with **multiple commits that should stay separate**: create a merge
   commit (GitHub merge method `merge`).
 - Never call GitHub's merge API without an explicit merge method, and never use `squash` or `rebase`.
+- When working on pull requests across the owner's repositories (e.g. merging Dependabot pull
+  requests), first check whether each repository is **archived** and skip archived ones entirely —
+  they're read-only, so their pull requests are to be ignored (no merging, no access requests).
 
 ## CI failures