Auto merge of #18217 - ChayimFriedman2:cast-unknown-ptr, r=Veykril

fix: Comment out cast checks for unknown ptr kind

Just like we don't check for types containing unknown.

Fixes #18214.

See also https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer/topic/Another.20case.20of.20.2318064.3F.

Author: bors