Add noexcept to cppgc::BasicPersistent's move assignment operator.

Change-Id: I9dbca09523644934eefb14fdb60f360b28417fa2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2983712Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75347}

include/cppgc/persistent.h

@@ -141,7 +141,7 @@ class BasicPersistent final : public PersistentBase,
   }
 
   // Move assignment.
-  BasicPersistent& operator=(BasicPersistent&& other) {
+  BasicPersistent& operator=(BasicPersistent&& other) noexcept {
     if (this == &other) return *this;
     Clear();
     PersistentBase::operator=(std::move(other));