fix: deduplicate PR comments for modified migrations

Check if a warning comment already exists before posting a new one.
This prevents duplicate comments when multiple commits are pushed to the PR.

.github/workflows/validate-migrations.sh

@@ -60,6 +60,16 @@ if [ -n "$MODIFIED_MIGRATIONS" ]; then
 
     # Post a PR review comment if running in GitHub Actions with a PR
     if [ -n "$GITHUB_TOKEN" ] && [ -n "$GITHUB_REPOSITORY" ] && [ -n "$PR_NUMBER" ]; then
+        # Check if a warning comment already exists to avoid duplicates
+        EXISTING_COMMENT=$(curl -s \
+            -H "Authorization: token $GITHUB_TOKEN" \
+            -H "Accept: application/vnd.github.v3+json" \
+            "https://api.github.com/repos/$GITHUB_REPOSITORY/issues/$PR_NUMBER/comments" \
+            | jq -r '.[] | select(.body | startswith("### ⚠️ Modified Migration Files Detected")) | .id' | head -1)
+
+        if [ -n "$EXISTING_COMMENT" ]; then
+            echo "Warning comment already exists (comment ID: $EXISTING_COMMENT), skipping"
+        else
             COMMENT_BODY="### ⚠️ Modified Migration Files Detected
 
 This PR modifies existing migration files that may have already been applied by users:
@@ -78,6 +88,7 @@ $(for m in $MODIFIED_MIGRATIONS; do echo "- \`$m\`"; done)
             echo "Posted PR comment about modified migrations"
         fi
     fi
+fi
 
 if [ "$HAS_ERRORS" = "true" ]; then
     echo ""