fix typo

Co-authored-by: Andy Fiddaman <andy@omnios.org>

library/std/src/sys/pal/unix/locks/pthread_mutex.rs

@@ -116,7 +116,7 @@ impl Mutex {
         // the lock call to never fail. Unfortunately however, some platforms
         // (Solaris) do not conform to the standard, and instead always provide
         // deadlock detection. How kind of them! Unfortunately that means that
-        // we need to check the error code here. To save use from UB on other
+        // we need to check the error code here. To save us from UB on other
         // less well-behaved platforms in the future, we do it even on "good"
         // platforms like macOS. See #120147 for more context.
         if r != 0 {