Follow-up to #2527360: Review all usages of Xss::filter(), Xss::filterAdmin(), and Html::escape()
We're using SafeMarkup::format in tests. We should not as this pollutes the safe string list and is irrelevant.
Where we are using it in $this->assertRaw() we should just convert it to a string. Where we are using it in an assertion message we should just convert it to a string with the variables inserted like "This is a $lol test".