Disable rebase workflow (apache#23943)

The change of the release workflow in apache#23928 removed the reason
why we should have rebase workflow possible. We only needed to
do rebase when we merged test branch into stable branch and
since we are doing it manually, there is no more reeason to
have it in the GitHub UI.

.asf.yaml

@@ -39,7 +39,7 @@ github:
   enabled_merge_buttons:
     squash: true
     merge: false
-    rebase: true
+    rebase: false
 
   protected_branches:
     main:

dev/README_RELEASE_AIRFLOW.md

@@ -224,16 +224,16 @@ The Release Candidate artifacts we vote upon should be the exact ones we vote ag
 
 - Update the `REVISION_HEADS_MAP` at airflow/utils/db.py to include the revision head of the release even if there are no migrations.
 - Commit the version change.
-- PR from the 'test' branch to the 'stable' branch, and manually merge it once approved. Here's how to manually merge the PR:
+- Check out the 'stable' branch
 
     ```shell script
-    git merge --ff-only v${VERSION_BRANCH}-test
+    git checkout v${VERSION_BRANCH}-stable
     ```
 
-- Check out the 'stable' branch
+- PR from the 'test' branch to the 'stable' branch, and manually merge it once approved. Here's how to manually merge the PR:
 
     ```shell script
-    git checkout v${VERSION_BRANCH}-stable
+    git merge --ff-only v${VERSION_BRANCH}-test
     ```
 
 - Tag your release