fix tool name in error

Change-Id: I7d898b0c309c01275645d2ae317c706c91f07a13
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/17600
Commit-Queue: Takuto Ikuta <tikuta@google.com>
Reviewed-by: Dirk Pranke <dpranke@google.com>

src/gn/ninja_copy_target_writer.cc

diff --git a/src/gn/ninja_copy_target_writer.cc b/src/gn/ninja_copy_target_writer.cc
index eca56d0..0ad7d67 100644
--- a/src/gn/ninja_copy_target_writer.cc
+++ b/src/gn/ninja_copy_target_writer.cc
@@ -38,7 +38,7 @@
       target_->toolchain()->GetTool(GeneralTool::kGeneralToolStamp);
   if (!stamp_tool) {
     g_scheduler->FailWithError(Err(
-        nullptr, "Copy tool not defined",
+        nullptr, "Stamp tool not defined",
         "The toolchain " +
             target_->toolchain()->label().GetUserVisibleName(false) +
             "\n used by target " + target_->label().GetUserVisibleName(false) +