Add merge conflict github PR check (#10812)

.github/workflows/merge-conflict-check.yml

@@ -0,0 +1,65 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+name: Github Merge Conflict Check
+
+on:
+  push:
+    branches: [main, dev, 1.0*, 2.0*, 3.0*, fasttrack/*]
+  pull_request:
+    branches: [main, dev, 1.0*, 2.0*, 3.0*, fasttrack/*]
+
+jobs:
+  spec-check:
+    name: Github Merge Conflict Check
+    runs-on: ubuntu-latest
+
+    steps:
+      # Checkout the branch of our repo that triggered this action
+      - name: Workflow trigger checkout
+        uses: actions/checkout@v4
+
+      - name: Get base commit for PRs
+        if: ${{ github.event_name == 'pull_request' }}
+        run: |
+          git fetch origin ${{ github.base_ref }}
+          echo "base_sha=$(git rev-parse origin/${{ github.base_ref }})" >> $GITHUB_ENV
+          echo "Merging ${{ github.sha }} into ${{ github.base_ref }}"
+
+      - name: Get base commit for Pushes
+        if: ${{ github.event_name == 'push' }}
+        run: |
+          git fetch origin ${{ github.event.before }}
+          echo "base_sha=${{ github.event.before }}" >> $GITHUB_ENV
+          echo "Merging ${{ github.sha }} into ${{ github.event.before }}"
+
+      - name: Check for merge conflicts
+        run: |
+          echo "Files changed: '$(git diff-tree --no-commit-id --name-only -r ${{ env.base_sha }} ${{ github.sha }})'"
+          changed_files=$(git diff-tree --diff-filter=d --no-commit-id --name-only -r ${{ env.base_sha }} ${{ github.sha }})
+
+          merge_conflict_found=false
+          for file in $changed_files ; do
+            if [ -f $file ]; then
+              echo "Checking for merge conflicts in $file"
+              if grep -H -r "^<<<<<<< HEAD$" $file; then
+                echo "Merge conflict found in $file"
+                merge_conflict_found=true
+              fi
+
+              if grep -H -r "^>>>>>>>$" $file; then
+                echo "Merge conflict found in $file"
+                merge_conflict_found=true
+              fi
+
+              if grep -H -r "^=======$" $file; then
+                echo "Merge conflict found in $file"
+                merge_conflict_found=true
+              fi
+            fi
+          done
+
+          if [[ $merge_conflict_found =~ [Tt]rue ]]; then
+            echo "Merge conflict found in one or more files"
+            exit 1
+          fi