chore: add warning for buildkite tool list update failure

Could not fetch tools from MCP server, added warning comment.

Co-authored-by: renovate[bot] <renovate[bot]@users.noreply.github.com>

Author: actions-user

registry/buildkite/spec.yaml

@@ -4,6 +4,8 @@
 # Original source: https://github.com/stacklok/toolhive
 # Import timestamp: 2025-08-14T07:27:00Z
 # ---
+# WARNING: Tool list fetch failed on 2025-08-21
+# Manual verification may be required
 name: buildkite
 description: Connect your Buildkite data (pipelines, builds, jobs, tests) to AI tooling and editors.
 tier: Official