dealerdirect/phpcodesniffer-composer-installer contains a Composer plugin which is blocked by your allow-plugins config. You may add it to the list if you consider it safe.
You can run "composer config --no-plugins allow-plugins.dealerdirect/phpcodesniffer-composer-installer [true|false]" to enable it (true) or disable it explicitly and suppress this exception (false)
See https://getcomposer.org/allow-plugins