fix test

tests/ui/atomic-from-mut-not-available.stderr

@@ -7,7 +7,7 @@ LL |     core::sync::atomic::AtomicU64::from_mut(&mut 0u64);
 note: if you're trying to build a new `AtomicU64`, consider using `AtomicU64::new` which returns `AtomicU64`
   --> $SRC_DIR/core/src/sync/atomic.rs:LL:COL
    = note: this error originates in the macro `atomic_int` (in Nightly builds, run with -Z macro-backtrace for more info)
-help: there is an associated function with a similar name
+help: there is an associated function `from` with a similar name
    |
 LL |     core::sync::atomic::AtomicU64::from(&mut 0u64);
    |                                    ~~~~