It's easily possible for Lua to raise errors where the string is not
valid UTF-8. When we turn that into a Scribunto_LuaError, we should
normalize it so other things don't break.
Bug: T208689
Change-Id: Idc5514261e99d64222b86877dd0500d425a26988
The following sniffs are failing and were disabled:
* MediaWiki.Commenting.MissingCovers.MissingCovers
Change-Id: I07b2cf945f44fd5532812a712f7dd40d2f208be2