Add workflow to check git conflict for backport PR

.github/workflows/check-conflict.yml

@@ -0,0 +1,41 @@
+#
+# Copyright (C) 2019-2024 vdaas.org vald team <[email protected]>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# You may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+name: Check conflict
+on:
+  pull_request:
+jobs:
+  dump-contexts-to-log:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./.github/actions/dump-context
+  check-conflict:
+    if: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.repo.fork == false }}
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          token: ${{ secrets.DISPATCH_TOKEN }}
+      - name: Set Git config
+        run: |
+          git config --global --add safe.directory ${GITHUB_WORKSPACE}
+      - name: Check conflict
+        run: |
+          if grep -r "<<<< HEAD" . --exclude-dir=.git --exclude=check-conflict.yml; then
+            echo "Please fix conflict locally."
+            exit 1
+          fi