fix: compile error (#28)

Author: ChaomingZhangCN

src/paimon/core/global_index/global_index_scan_impl.h

@@ -47,13 +47,13 @@ class GlobalIndexScanImpl : public GlobalIndexScan {
         return snapshot_;
     }
 
- private:
-    Status Scan();
-
     Result<std::optional<std::shared_ptr<GlobalIndexResult>>> ParallelScan(
         const std::vector<Range>& ranges, const std::shared_ptr<Predicate>& predicate,
         const std::shared_ptr<Executor>& executor);
 
+ private:
+    Status Scan();
+
  private:
     bool initialized_ = false;
     std::shared_ptr<MemoryPool> pool_;