Restore option_env!("CARGO_PKG_VERSION")

Make repo match crate archive contents.

Bug: http://b/339424309
Test: treehugger
Change-Id: I6f9c9f564c0a570b7303e8b95a77fbd271d9f83d

lib.rs

diff --git a/lib.rs b/lib.rs
index 4a177ef..c4ab114 100644
--- a/lib.rs
+++ b/lib.rs
@@ -933,7 +933,7 @@
 
         if !self.options.disable_header_comment {
             let version =
-                Some("0.69.5").unwrap_or("(unknown version)");
+                option_env!("CARGO_PKG_VERSION").unwrap_or("(unknown version)");
             writeln!(
                 writer,
                 "/* automatically generated by rust-bindgen {version} */{NL}",