extract_proto output_prefix flag fix.

tools/extract_proto/extract_proto.cc

diff --git a/tools/extract_proto/extract_proto.cc b/tools/extract_proto/extract_proto.cc
index 2dffd87..ea31bb0 100644
--- a/tools/extract_proto/extract_proto.cc
+++ b/tools/extract_proto/extract_proto.cc
@@ -107,7 +107,7 @@
 
 struct OutputConfig {
   std::filesystem::path output_folder;
-  std::string_view output_prefix;
+  std::string output_prefix;
   bool output_as_text_proto;
   int limit;
 };