Ideally, we would like to test against 8.5 too. I'd suggest to add symfony 8 in the symfony-version and add to exclude testing against php < 8.4

Indeed, that's a better alternative.

However, I had to modify the composer config minimum-stability dev step to run when we try to install a dev version of Symfony. Maybe I missed something with the matrix configuration, but it's not possible to only configure the old matrix.minimum-stability config only when using Symfony 8.0.x-dev, right?

@Kocal it is possible. GA supports if condition.

As an example you could take a look at the PR #1892 and what we did there in order to introduce Symfony 7.0 support

I mean, directly with the matrix, like I was able to do with include from the 1st commit.

It should be fine now, I see that some Symfony 8 packages are installed in https://github.com/infection/infection/actions/runs/19081901778/job/54512486280?pr=2551, but there is still PHPBench that force Symfony 7.x for symfony/console or symfony/filesystem for example.