Add a PR check to check for conflict markers

This check is primarily intended to validate that any merge conflicts in
the v2 -> v1 backport PR are fixed before the PR is merged.

.github/workflows/check-for-conflicts.yml

@@ -0,0 +1,31 @@
+# Checks for any conflict markers created by git. This check is primarily intended to validate that
+# any merge conflicts in the v2 -> v1 backport PR are fixed before the PR is merged.
+name: Check for conflicts
+
+on:
+  pull_request:
+    branches: [main, v1, v2]
+    # Run checks on reopened draft PRs to support triggering PR checks on draft PRs that were opened
+    # by other workflows.
+    types: [opened, synchronize, reopened, ready_for_review]
+
+jobs:
+  check-for-conflicts:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Check for conflicts
+        run: |
+          # Use `|| true` since grep returns exit code 1 if there are no matches, and we don't want
+          # this to fail the workflow.
+          FILES_WITH_CONFLICTS=$(grep --extended-regexp --ignore-case --line-number --recursive \
+            '^(<<<<<<<|>>>>>>>)' . || true)
+          if [[ "${FILES_WITH_CONFLICTS}" ]]; then
+            echo "Fail: Found merge conflict markers in the following files:"
+            echo ""
+            echo "${FILES_WITH_CONFLICTS}"
+            exit 1
+          else
+            echo "Success: Found no merge conflict markers."
+          fi