CI HACK: Truncate compile-fail stderr to match broken CI runs

https://github.com/erickt/rust-zmq/actions/runs/12294855109/job/34310502917

Author: MarijnS95

tests/compile-fail/socket-thread-unsafe.stderr

@@ -23,9 +23,3 @@ note: required because it's used within this closure
    |                           ^^^^^^^
 note: required by a bound in `spawn`
   --> $RUST/std/src/thread/mod.rs
-   |
-   | pub fn spawn<F, T>(f: F) -> JoinHandle<T>
-   |        ----- required by a bound in this function
-...
-   |     F: Send + 'static,
-   |        ^^^^ required by this bound in `spawn`