The phpstan job fails when core-dev does not include the phpstan package

Migrated issue

Reported by: avpaderno

Related to !370 (merged)

I was testing a merge request for the contrib Seven theme, for which I set the composer job to require Drupal 9.5.11.

The phpstan job returned these errors.

$ php $CI_PROJECT_DIR/vendor/bin/phpstan --version
Could not open input file: /builds/project/seven/vendor/bin/phpstan
...
WARNING: junit.xml: no matching files. Ensure that the artifact path is relative to the working directory (/builds/project/seven) 
WARNING: phpstan-baseline.neon: no matching files. Ensure that the artifact path is relative to the working directory (/builds/project/seven) 
WARNING: phpstan-quality-report.json: no matching files. Ensure that the artifact path is relative to the working directory (/builds/project/seven) 

drupal/core-dev 9.5.11 does not require phpstan/phpstan, contrary to drupal/core-dev 10.