cppgc: Fix compilation error on gcc

Fixing a dcheck compilation error missed by
https://crrev.com/c/3302850

Change-Id: I98c7394cbe64d99647656aebd175c8321f53c2de
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3300927Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/main@{#78112}

src/heap/cppgc/heap.cc

@@ -120,7 +120,7 @@ void Heap::CollectGarbage(Config config) {
 
 void Heap::StartIncrementalGarbageCollection(Config config) {
   DCHECK_NE(Config::MarkingType::kAtomic, config.marking_type);
-  DCHECK_NE(marking_support_, MarkingType::kAtomic);
+  DCHECK_NE(marking_support_, Config::MarkingType::kAtomic);
   CheckConfig(config, marking_support_, sweeping_support_);
 
   if (IsMarking() || in_no_gc_scope()) return;