Allow unused_imports of errors from lib

Summary:
This lint started happening with Rust 1.75.0 because of
rust-lang/rust#116033

Sometimes `errors` might be empty, sometimes not (I think?). So suppress
the lints.

Reviewed By: dtolnay

Differential Revision: D52958558

fbshipit-source-id: 5240a22e1d17de9f41d34c70d77016a3e3324f66

Author: zertosh

thrift/compiler/generate/templates/rust/lib.rs.mustache

@@ -33,6 +33,7 @@ include!("{{program:include_src}}");
 {{#program:constants?}}
 pub use self::consts::*;
 {{/program:constants?}}
+#[allow(unused_imports)]
 pub use self::errors::*;{{!
 }}{{#program:types?}}
 pub use self::types::*;{{!