[3.8] bpo-41898: add caveat on root logger seeing all messages in assertLogs doc (GH-22526)#22537

vsajip merged 1 commit intopython:3.8python/cpython:3.8from

miss-islington:backport-1ed5443-3.8miss-islington/cpython:backport-1ed5443-3.8Copy head branch name to clipboard