Fix misfire of compaction read barrier

gc_compact_move incorrectly returns false when destination heap is full
after sweeping. It returns false even if destination heap is different
than source heap (returning false means that the source heap has
finished compacting). This causes the source page to get locked, which
causes a read barrier fire when we try to compact the source heap again.

gc.c

@@ -8519,7 +8519,7 @@ gc_compact_move(rb_objspace_t *objspace, rb_heap_t *heap, rb_size_pool_t *size_p
 
         dheap->sweeping_page = ccan_list_next(&dheap->pages, dheap->sweeping_page, page_node);
         if (gc_compact_heap_cursors_met_p(dheap)) {
-            return false;
+            return dheap != heap;
         }
     }