TASK: Migrate to PHPStan (adjustments in Flow 9)

[mhsdesign]

With #3218 PHPStan level 1 was added to the whole Flow code base and CI for Flow 8. This upmerged change needs some adjustments to pass the CI in Flow 9

• fix types in code that was introduced with Flow 9
• fix types where neos depends on it (by correcting types and adding never)
• adjust unit test as never cannot be doubled (eventually this will be fixed via: Methods that return never cannot be doubled sebastianbergmann/phpunit#5048)
• fix ci and style as neos 9 followup for TASK: Migrate to PHPStan for Flow 8 #3218

Checklist

• Code follows the PSR-2 coding style
• Tests have been created, run and adjusted as needed
• The PR is created against the lowest maintained branch
• Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• Reviewer - The first section explains the change briefly for change-logs
• Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[kitsunet]

Mmm, but like in 9.0? I think this will make upmerges harder than they already are with the many chnages in this major version, I would rather do it in 8.0 maybe? In the hopes that we don't upmerge 7.3 all that much anymore...

[mhsdesign]

Draft as we probably want to target 8.0 #3218

Things that are not included there:

Adding never as return type

[kdambekalns]

Nice, I think. But I'd like to see the deprecation removals in their own commit, at least. Otherwise they are camouflaged a bit too much…