build: Upgrade mediawiki-codesniffer from 26.0.0 to 28.0.0

Newly-disabled general rules:
* MediaWiki.Commenting.FunctionComment.MissingSplatVariadicArg
* MediaWiki.Commenting.FunctionComment.SuperfluousVariadicArgComment
* MediaWiki.Commenting.PhpunitAnnotations.ForbiddenExpectedException
* MediaWiki.Commenting.PhpunitAnnotations.ForbiddenExpectedExceptionMessage
* MediaWiki.Commenting.PhpunitAnnotations.ForbiddenExpectedExceptionMessageRegExp
* MediaWiki.Usage.NullableType.PHP71NullableStyle
* MediaWiki.Usage.PHPUnitTypeHints.MissingTypehint
* PSR12.Files.ImportStatement.LeadingSlash
* PSR12.Properties.ConstantVisibility.NotFound

Change-Id: Ifcf8c6d5fecc47a32741114b5a5b746a41510045