Add an auto-generated header

src/tests/compat_parse.rs

@@ -1,3 +1,7 @@
+// WARNING
+// This file was auto-generated using the `build_tests.py` script.
+// Please do not edit it manually.
+
 use chrono::SecondsFormat;
 
 use parse;

src/tests/compat_split_string.rs

@@ -1,3 +1,7 @@
+// WARNING
+// This file was auto-generated using the `build_tests.py` script.
+// Please do not edit it manually.
+
 use Token;
 use tokenize;