[NFC] Fixes -Wrange-loop-analysis warnings

This avoids new warnings due to D68912 adds -Wrange-loop-analysis to -Wall.

Differential Revision: https://reviews.llvm.org/D71857
diff --git a/clang/lib/Tooling/ASTDiff/ASTDiff.cpp b/clang/lib/Tooling/ASTDiff/ASTDiff.cpp
index 00db770..4d49522 100644
--- a/clang/lib/Tooling/ASTDiff/ASTDiff.cpp
+++ b/clang/lib/Tooling/ASTDiff/ASTDiff.cpp
@@ -787,7 +787,7 @@
     return;
   ZhangShashaMatcher Matcher(*this, T1, T2, Id1, Id2);
   std::vector<std::pair<NodeId, NodeId>> R = Matcher.getMatchingNodes();
-  for (const auto Tuple : R) {
+  for (const auto &Tuple : R) {
     NodeId Src = Tuple.first;
     NodeId Dst = Tuple.second;
     if (!M.hasSrc(Src) && !M.hasDst(Dst))