Update composer.json

Upgraded static analyzers

Fix for PHPUnit 8 compatibility

Added support for PHP 8.1 (vlucas#496)

Make Validator::assert and Validator::assertNullable public

Updated static analyzers

Merge branch '2.6' into 3.6

Revert "Test on PHP 8.1 too (vlucas#467)"

This reverts commit 692830c.

Support boolean values in $_ENV and $_SERVER (vlucas#457)

Merge branch '5.0'