CI: Add testrun for "psr/http-message" v2 with slim

[Chris53897]

in composer.json "psr/http-message" v1 and v2 are allowed.

But if i see this correct, v2 is never tested in the testruns. Example: https://github.com/php-http/message/actions/runs/7623563875/job/20763848547

Because of Version 3 of "slim/slim" https://github.com/php-http/message/blob/1.x/composer.json#L31C10-L31C19

https://packagist.org/packages/slim/slim#3.12.5

Only the dev-version supports v1 and v2 https://packagist.org/packages/slim/slim#4.x-dev