Allow ocramius/package-versions plugin

Fixes the following error:
  Error: ocramius/package-versions contains a Composer plugin which is blocked by your allow-plugins config. You may add it to the list if you consider it safe.

See https://getcomposer.org/allow-plugins

Add "setting" to the PHPUnit list of requirements

See sebastianbergmann/phpunit#2967

Apply a workaround for the psalm bug

See vimeo/psalm#6009

Tweak tests

Move the automatic expectation verification from trait to test case

Update .gitattributes