A continuation of PR #3859. Change code that would be flagged if we were to run Phpstan at level 9 (we currently run level 8). I may or may not follow up with source code (454 level-9 problems remain for src), but there is no reason to avoid the effort for samples.
No changes are made to src.
Because they tend to clutter our code a lot and unfortunately, there are
lots of false positives. Instead, it would probably be better to deal
with false positives out of band, via the Scrutinizer web UI.