While this is not strictly required, because removal will
happen in PHPUnit 9.0, we are already getting rid of all
uses in core.

From release notes:https://phpunit.de/announcements/phpunit-8.html

assertInternalType() is deprecated and will be removed in
PHPUnit 9. Refactor your test to use assertIsArray(), assertIsBool(),
assertIsFloat(), assertIsInt(), assertIsNumeric(), assertIsObject(),
assertIsResource(), assertIsString(), assertIsScalar(),
assertIsCallable(), or assertIsIterable() instead.