* DeprecatedHooksTest: Don't use assertContains().
* Replace uses of deprecated asserts:
- assertFileNotExists() -> assertFileDoesNotExist()
* Update hierarchy of MediaWikiPHPUnitResultPrinter, since ResultPrinter
is an interface in PHPUnit 9.
* Remove temporary forward-compat methods.
* Remove directories that don't exist from tests/phpunit/suite.xml, since
they now make PHPUnit exit:
- tests/phpunit/skins, it used to have SideBarTest, then moved to
tests/phpunit/includes/skins
- tests/phpunit/documentation, it used to have ReleaseNotesTest, then
moved to tests/phpunit/unit/documentation
* Update configuration with --migrate-configuration and reformat.
* Avoid redefining getMockBuilder() in
ActionModuleBasedHandlerTestTrait, use a @method annotation instead.
* In RCCacheEntryFactoryTest, avoid using internal PHPUnit logic for
HTML validation, and use native PHP methods instead. The code was
copied from Xml::load (moved to \Xml\Loader::load in PHPUnit 9) and
simplified for this use case.
Bug: T243600
Bug: T262076
Change-Id: I851b9158b73d0cfc315eed9d63b15c54b05895e3
