Add link to clippy::thread_local_initializer_can_be_made_const bug report

rust-lang/rust-clippy#12404

Author: taiki-e

tests/repr_packed.rs

@@ -4,7 +4,7 @@
 // https://github.com/rust-lang/rust/pull/82525
 #![allow(unknown_lints, renamed_and_removed_lints)]
 #![forbid(unaligned_references, safe_packed_borrows)]
-#![allow(clippy::thread_local_initializer_can_be_made_const)] // clippy bug: this lint doesn't consider MSRV
+#![allow(clippy::thread_local_initializer_can_be_made_const)] // clippy bug: this lint doesn't consider MSRV: https://github.com/rust-lang/rust-clippy/issues/12404
 
 use std::cell::Cell;