gh-103109: Document ignore_warnings() test support helper (GH-103110) (cherry picked from commit 32937d6aa414ec7db5c63ef277f21db1880b3af4) Co-authored-by: Charlie Zhao <zhaoyu_hit@qq.com> Co-authored-by: C.A.M. Gerlach <CAM.Gerlach@Gerlach.CAM>