ci: prevent v2 release sync to main

.github/workflows/staging-step-3.yml

@@ -1,11 +1,11 @@
-name: "Staging Release - Step 3: Release to CDN and Synchronize Branches"
+name: "Staging Release - Step 3: Release to CDN and Synchronize v2 Branches"
 
 on:
     workflow_dispatch:
 
 jobs:
     synchronize-branches:
-      name: Synchronize SDK to all branches
+      name: Synchronize SDK to v2 branches
       runs-on: ubuntu-latest
       env:
         GITHUB_TOKEN: ${{ secrets.MP_SEMANTIC_RELEASE_BOT }}
@@ -27,14 +27,13 @@ jobs:
           run: |
             git push origin HEAD:development
 
-        # We will eventually replace master with main
-        - name: Push release commits to main and master
+        # main is the v3 release line. Do not push v2 release commits to it.
+        - name: Push release commits to master
           run: |
             git push origin HEAD:master
-            git push origin HEAD:main
 
         - name: Push release commits to Release Order Branches
           run: |
             git push origin HEAD:release-order-a
             git push origin HEAD:release-order-b
-            git push origin HEAD:release-order-c
+            git push origin HEAD:release-order-c