Merge pull request #703 from MetRonnie/actions

GH Actions: add branch sync workflow

.github/workflows/branch_sync.yml

@@ -0,0 +1,20 @@
+name: Sync PR
+
+on:
+  push:
+    branches:
+      - '8.*.x'
+  schedule:
+    - cron: '11 11 * * 7' # every Sunday at 11:11
+  workflow_dispatch:
+    inputs:
+      head_branch:
+        description: Branch to merge into master
+        required: true
+
+jobs:
+  sync:
+    uses: cylc/release-actions/.github/workflows/branch-sync.yml@v1
+    with:
+      head_branch: ${{ inputs.head_branch }}
+    secrets: inherit