ci: keep release candidate in draft for tests before tag (#567)

ci: create release PR as draft

Co-authored-by: Claude <svc-devxp-claude@slack-corp.com>
Co-authored-by: Michael Brooks <mbrooks@slack-corp.com>

Author: 3 people

.github/workflows/release.yml

@@ -131,6 +131,6 @@ jobs:
             gh pr edit "$EXISTING_PR" --title "$PR_TITLE" --body "$PR_BODY" --milestone "Next Release" --add-label "release" --add-label "semver:${SEMVER}"
             echo "Updated PR #$EXISTING_PR"
           else
-            gh pr create --head rc --base main --title "$PR_TITLE" --body "$PR_BODY" --milestone "Next Release" --add-label "release" --add-label "semver:${SEMVER}"
+            gh pr create --draft --head rc --base main --title "$PR_TITLE" --body "$PR_BODY" --milestone "Next Release" --add-label "release" --add-label "semver:${SEMVER}"
             echo "Created new release PR"
           fi