Fix interrupt-invalid.rs on stable

Author: jonas-schievink

cortex-m-rt/tests/compile-fail/interrupt-invalid.rs

@@ -19,4 +19,4 @@ enum interrupt {
 // NOTE this looks a bit better when using a device crate:
 // "no variant named `foo` found for type `stm32f30x::Interrupt` in the current scope"
 #[interrupt]
-fn foo() {} //~ ERROR no variant named `foo` found for type `interrupt` in the current scope
+fn foo() {} //~ ERROR no variant or associated item named `foo` found for type `interrupt` in the current scope