Allow unknown lint in cortex-m-semihosting.

Author: thejpster

cortex-m-semihosting/src/export.rs

@@ -3,6 +3,8 @@
 // This must be replaced by a different solution before rust edition 2024
 // https://doc.rust-lang.org/nightly/edition-guide/rust-2024/static-mut-references.html
 #![allow(static_mut_refs)]
+// the above lint is not known in our MSRV, so allow unknown lints
+#![allow(unknown_lints)]
 
 use core::fmt::{self, Write};