MWPopupTool: Don't assume editnotice html has a single wrapping element
In case of FlaggedRevs, for example, the software is given a loose
string of html with a Bold element, Text nodes, and Anchor element.
Bug: T95989
Change-Id: I3d345677507ffc08feec0f7785e148ac98f19cb7
(cherry picked from commit 66c9d538c504f5cd79061e869020768a0a2cf751)