Run static code analysis on GitHub Actions

[fbourigault]

Q	A
Branch?	2.x
Bug fix?	no
New feature?	no
BC breaks?	no
Deprecations?	no
Tests pass?	yes
Fixed tickets
License	MIT
Doc PR

As discussed with @dbu, here is a PR to replace most of Scrutinizer work with static code analysis.

I choose PHPStan as I use it daily at work and it's the tool used by SonataAdminBundle which is my main source of inspiration for all my GitHub Actions PRs.

[coveralls]

Coverage remained the same at 83.645% when pulling d68b9be on fbourigault:github-actions-phpstan into db366d2 on liip:2.x.

[fbourigault]

With current implementation, phpstan can be installed with a newer version in an unrelated PR.

This could lead to unrelated build failures.

What are our options to lock phpstan to a given version?

EDIT:
I looked at SonataAdminBundle and they don't do anything. We can merge this one and improve things if it gets annoying.

[lsmith77]

there seems to be a minor conflict.

[lsmith77]

for a sub 1.0 dependency on a require-dev I am totally fine locking for a specific version.

[dbu]

sorry for the late reply. looks good to me, thanks a lot for the work! didn't know about the phpstan stub functionality, that is quite neat (i always made it ignore the warnings about unknown classes, with a comment that this was legacy support. much better and safer with the stubs thing!)

i will rebase the branch to solve conflicts and then merge.

[dbu]

thanks! i rebased and solved conflicts in #1390 but unfortunately a couple of failures now show