[BUGFIX] Avoid crash during interface checks on non-existing classes (#5984)
[BUGFIX] Avoid crash during interface checks on non-existing classes (#5984)

`ClassLikes::classImplements(NonExisting::class, WellKnown::class)`
now returns `false` instead of throwing an exception for non-existing
classes.

Fixes: #5983
vimeo/psalm,vimeo/psalm