Problem 1
- Root composer.json requires phpunit/phpunit dev-main -> satisfiable by phpunit/phpunit[dev-main].
- Root composer.json requires vimeo/psalm dev-master -> satisfiable by vimeo/psalm[dev-master].
- phpunit/phpunit dev-main requires sebastian/diff ^8.0 -> satisfiable by sebastian/diff[8.0.x-dev (alias of dev-main)].
- vimeo/psalm dev-master requires sebastian/diff ^4.0 || ^5.0 || ^6.0 || ^7.0 -> satisfiable by sebastian/diff[4.0.0, ..., 4.0.x-dev, 5.0.0, ..., 5.1.x-dev, 6.0.0, 6.0.1, 6.0.2, 6.0.x-dev, 7.0.0, 7.0.x-dev].
- You can only install one version of a package, so only one of these can be installed: sebastian/diff[dev-main, 4.0.0, ..., 4.0.x-dev, 5.0.0, ..., 5.1.x-dev, 6.0.0, 6.0.1, 6.0.2, 6.0.x-dev, 7.0.0, 7.0.x-dev].
- sebastian/diff 8.0.x-dev is an alias of sebastian/diff dev-main and thus requires it to be installed too.
