IWYU: Added missing include: include/cppgc/persistent.h

This missing include was undetected because trace_perf.cc is only
built if the checkout_google_benchmark custom gclient variable is
defined.

Bug: none
Change-Id: If2016edad4df382f14903593ea18066f7759c4d5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2698387Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Chris Mumford <cmumford@google.com>
Cr-Commit-Position: refs/heads/master@{#72825}

test/benchmarks/cpp/cppgc/trace_perf.cc

@@ -4,6 +4,7 @@
 
 #include "include/cppgc/allocation.h"
 #include "include/cppgc/garbage-collected.h"
+#include "include/cppgc/persistent.h"
 #include "src/heap/cppgc/globals.h"
 #include "src/heap/cppgc/heap.h"
 #include "test/benchmarks/cpp/cppgc/utils.h"