Add proto file for unwrap test (#25)

Author: AdrienVannson

tests/inputs/unwrap/unwrap.proto

@@ -0,0 +1,11 @@
+syntax = "proto3";
+
+package unwrap;
+
+message NestedMessage {
+    int32 x = 1;
+}
+
+message Message {
+    NestedMessage x = 1;
+}