Rollup merge of #122091 - ChrisDenton:comment, r=RalfJung

Note why we're using a new thread in `test_get_os_named_thread`

``@RalfJung`` expressed some "surprise and confusion" about why we're spawning a new thread in this test. Hopefully this comment will help future readers.

library/std/src/thread/tests.rs

@@ -80,6 +80,7 @@ fn test_named_thread_truncation() {
 #[test]
 fn test_get_os_named_thread() {
     use crate::sys::thread::Thread;
+    // Spawn a new thread to avoid interfering with other tests running on this thread.
     let handler = thread::spawn(|| {
         let name = c"test me please";
         Thread::set_name(name);