Labels have incorrect links in merge request system notes about label changes

Similar to #15402 (closed) but limited to system notes.

!30428 (merged) fixed this for other types of notes, but we also need to provide label_url_method in the banzai_render_context of ResourceLabelEvent: https://gitlab.com/gitlab-org/gitlab/blob/4ee3412aab6bd5b67ee45f8e60e50199feb80381/app/models/resource_label_event.rb#L57

Steps to Reproduce

1. Create / open an existing MR
2. Make some label changes
3. On the system note about the label change, clicking on the labels lead to https://gitlab.com/some_group/some_project/issues?label_name%5B%5D=XXX instead of https://gitlab.com/some_group/some_project/merge_requests?label_name%5B%5D=XXX