internal/testprotos: fix import path of test.proto

Change the go_package option to match the actual import path of this package.

Change-Id: Ie8630878ce75e34ca76d97c6e2922254cf964801
Reviewed-on: https://go-review.googlesource.com/c/156344
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
diff --git a/internal/testprotos/test/test.proto b/internal/testprotos/test/test.proto
index fcb4174..bfcd3a6 100644
--- a/internal/testprotos/test/test.proto
+++ b/internal/testprotos/test/test.proto
@@ -6,7 +6,7 @@
 
 package goproto.proto.test;
 
-option go_package = "github.com/golang/protobuf/v2/proto/testpb";
+option go_package = "github.com/golang/protobuf/v2/internal/testprotos/test";
 
 message TestAllTypes {
   message NestedMessage {