query/plumbing: adjust comment to reality

Author: RalfJung

compiler/rustc_middle/src/query/plumbing.rs

@@ -319,7 +319,7 @@ macro_rules! define_callbacks {
 
 pubtypeStorage<'tcx> = <$($K)*as keys::Key>::Cache<Erase<$V>>;
 
-// Ensure that keys grow no larger than 72 bytes by accident.
+// Ensure that keys grow no larger than 80 bytes by accident.
 // Increase this limit if necessary, but do try to keep the size low if possible
  #[cfg(target_pointer_width = "64")]
 const _:() = {