Fix compile error preventing tests from running.

With this, the code now compiles irrespective of whether our crate is
called bindgen or autocxx_bindgen.

Author: martinboehme

tests/parse_callbacks/mod.rs

@@ -1,4 +1,4 @@
-use bindgen::callbacks::*;
+use crate::bindgen::callbacks::*;
 
 #[derive(Debug)]
 struct EnumVariantRename;