Fix validation errors for timestamps in GitHub syncing to not error but ignore

# Problem

Right now if there are validation errors due to timestamps being off in GitHub syncing, it appears we're seeing `validating_tasks` or `validating_comments` errors. What we should do instead is actually ensure that if the timestamps are off, that we instead say the event payload was ignored due to timestamp differences.

Start by tracing the validating_tasks and validating_comments errors in the GitHub syncing flow. Identify where timestamp validation failures are handled. Done means timestamp differences cause the event payload to be ignored with the stated explanation instead of producing validation errors.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.