Flip direction of the 6.3 merge workflow

Author: owenv

.github/workflows/automerge.yml

@@ -15,8 +15,8 @@ jobs:
     name: Create PR to merge release into main branch
     uses: swiftlang/github-workflows/.github/workflows/create_automerge_pr.yml@main
     with:
-      head_branch: release/6.3
-      base_branch: main
+      head_branch: main
+      base_branch: release/6.3
     permissions:
       contents: write
       pull-requests: write