Immix needs post_scan. Fix style check

Author: qinsoon

src/plan/global.rs

@@ -564,8 +564,8 @@ pub struct CommonPlan<VM: VMBinding> {
     pub immortal: ImmortalSpace<VM>,
     #[space]
     pub los: LargeObjectSpace<VM>,
-    // TODO: We should use a marksweep space for nonmoving.
     #[space]
+    #[cfg_attr(not(any(feature = "immortal_as_nonmoving", feature = "marksweep_as_nonmoving")), post_scan)] // Immix space needs post_scan
     pub nonmoving: NonMovingSpace<VM>,
     #[parent]
     pub base: BasePlan<VM>,

src/policy/immix/immixspace.rs

@@ -232,6 +232,7 @@ impl<VM: VMBinding> crate::policy::gc_work::PolicyTraceObject<VM> for ImmixSpace
         }
     }
 
+    #[allow(clippy::if_same_then_else)] // DEFAULT_TRACE needs a workaround which is documented below.
     fn may_move_objects<const KIND: TraceKind>() -> bool {
         if KIND == TRACE_KIND_DEFRAG {
             true