fix: #3630532 by andres-alvarez: Fix PHPStan readonly constructor and...

fix: #3630532 by andres-alvarez: Fix PHPStan readonly constructor and deprecated filter_default_format()

DependencySerializationTrait::__wakeup() cannot initialize a readonly property declared in a child class on PHP < 8.4, so the promoted renderer property in the two confirm forms is no longer readonly. The functional tests called filter_default_format(), deprecated in 11.4.0; the FilterFormatRepositoryInterface replacement does not exist before 11.4 and the module supports ^10.3, so the tests use the plain_text fallback format that the call resolved to there.

Related to #3630532