Fix tsan options_test (#7845)

Summary:
Minor tsan issue that counter could be bumped concurrently:
https://app.circleci.com/pipelines/github/facebook/rocksdb/5431/workflows/79312c7c-5815-4f07-8836-94625db8e33e/jobs/81619

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7845

Reviewed By: akankshamahajan15

Differential Revision: D25851472

Pulled By: jay-zhuang

fbshipit-source-id: 74cc8797ac503413bec27a30e5d1f055379777e8

db/db_options_test.cc

@@ -190,10 +190,11 @@ TEST_F(DBOptionsTest, SetWalBytesPerSync) {
   options.env = env_;
   Reopen(options);
   ASSERT_EQ(512, dbfull()->GetDBOptions().wal_bytes_per_sync);
-  int counter = 0;
+  std::atomic_int counter{0};
   int low_bytes_per_sync = 0;
   ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->SetCallBack(
-      "WritableFileWriter::RangeSync:0", [&](void* /*arg*/) { counter++; });
+      "WritableFileWriter::RangeSync:0",
+      [&](void* /*arg*/) { counter.fetch_add(1); });
   ROCKSDB_NAMESPACE::SyncPoint::GetInstance()->EnableProcessing();
   const std::string kValue(kValueSize, 'v');
   int i = 0;