Fix sync workflow to only trigger on v12.0 pushes and add concurrency control (#827)

## Problem

The current sync workflow triggers on pushes to both `v12.0` and `v13.0`
branches but always merges `v12.0` → `v13.0` regardless of which branch
triggered it. This causes:

- **Redundant runs** when pushing to `v13.0` (since it doesn't need to
sync anywhere)
- **Noisy executions** that provide no value
- **Potential race conditions** from concurrent sync operations

The goal is one-way forward sync only: changes to `v12.0` should merge
into `v13.0`, but changes to `v13.0` should not trigger the workflow.

## Solution

Updated `.github/workflows/sync-version-branches.yml` to implement
proper one-way sync:

### Key Changes

1. **Refined triggers**: Now only triggers on pushes to `v12.0` branch
(removed `v13.0`)
2. **Manual dispatch**: Added `workflow_dispatch` for manual runs when
needed
3. **Concurrency control**: Added concurrency group `sync-v12-to-v13`
with `cancel-in-progress: true` to prevent overlapping operations
4. **Improved clarity**: Updated names to clearly indicate the sync
direction
   - Workflow: "Sync v12.0 -> v13.0"
   - Step: "Keep v13.0 in sync with v12.0"

### Preserved Settings

- ✅ Same action version (`jojomatik/[email protected]`)
- ✅ Same merge strategy and conflict resolution settings
- ✅ Same bot credentials and GitHub token usage

## Benefits

- **Eliminates noise**: No more unnecessary runs on `v13.0` pushes
- **Prevents conflicts**: Concurrency control ensures operations don't
interfere
- **Maintains pattern**: Clean one-way forward sync from older to newer
versions
- **Manual control**: Allows manual triggering when needed

## Testing

- Validated YAML syntax and structure
- Confirmed compatibility with GitHub Actions workflow schema
- Verified all required fields and job configurations are present
- Follows existing repository YAML formatting standards

After merging, pushes to `v12.0` will trigger the sync to `v13.0`, while
pushes to `v13.0` will not trigger any sync operations.

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---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: BenjaminMichaelis <[email protected]>

Author: Copilot

.github/workflows/sync-version-branches.yml

@@ -1,14 +1,20 @@
-name: Sync branches
+name: Sync v12.0 -> v13.0
 on:
   push:
-    branches: [ 'v12.0', 'v13.0' ]
+    branches:
+      - 'v12.0'
+  workflow_dispatch:
+
+concurrency:
+  group: sync-v12-to-v13
+  cancel-in-progress: true
 
 jobs:
   sync_branches:
     name: Sync Branches
     runs-on: ubuntu-latest
     steps:
-      - name: Keep branches in sync
+      - name: Keep v13.0 in sync with v12.0
         uses: jojomatik/[email protected]
         with:
           source: "v12.0"
@@ -17,7 +23,4 @@ jobs:
           resolve_conflicts: "false"
           git_committer_name: 'BenjaminMichaelisBot'
           git_committer_email: '[email protected]'
-          # The access token to push to the repository
-          #   Optional
-          #   Default: github.token
-          github_token: ${{ secrets.GIT_PUSHTOKEN }}
+          github_token: ${{ secrets.GIT_PUSHTOKEN }}