DX: Faster feedback loop: stop running `phpstan` twice for local development: ~30s → ~15s, only run twice on CI instead (currently 4!)

Overview

#3591245: DX: Introduce `composer run lint` that runs PHPCS + PHPStan (sibling to `npm run lint`) improves the DX, and makes it consistent between PHP (composer run …) and everything else (npm run …).

#3538439: Running tests locally is difficult to match with the CI introduced composer run phpstan and immediately optimized it for running on CI: it set up caching, then runs it twice.

(Meaning the intent is the same as #3589565: Make `npm run lint` output easier for humans to parse: optimize this for developer use, rather than CI.)

Proposed resolution

Make composer run phpstan run it only once, this makes a very noticeable difference (with caches primed, i.e. as you would use this during development):

HEAD: ~30 seconds

$ time composer run phpstan
…
real	0m18.920s
user	0m7.768s
sys	0m12.244s

MR: ~15 seconds

$ time composer run phpstan
…
real	0m8.723s
user	0m3.655s
sys	0m5.315s

User interface changes

None.