Add `ext-psr` to "conflict" section in composer.json

[vjik]

The psr PHP extension is designed to work with psr/log version 1.0.0, but Yii Log works with psr/log version 2 or higher.

PECL page: https://pecl.php.net/package/psr
Extension repo: https://github.com/jbboehr/php-psr