Skip AWS preview deploys for forked pull requests

[moeboua-cloud]

Fixes #1099

[claude]

Claude Code Review

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[moeboua-cloud]

#1097 is the second blocker. It stops the AWS preview deploy from failing on forked PRs.

[moeboua-cloud]

These two workflow PRs unblock forked contributor PRs. Right now forked PRs are failing due to checkout behavior in prettier/slinky and AWS preview deploy behavior on forked PRs, which is also preventing unrelated docs PRs from passing checks. If these merge first, PRs #1093 and #1094 should be able to rerun with a much cleaner path.

[moeboua-cloud]

This PR is intended to unblock forked contributor pull requests in this repository. Related issues are tracked in #1098 and #1099. If these workflow fixes can merge first, they should remove CI noise affecting other open docs PRs from forked branches.