Mark std::process:Child as #[must_use]

Simply dropping this is usually a bad idea, for the reasons
extensively discussed in the documentation.

Closes: #70186
Signed-off-by: Ian Jackson <[email protected]>

Author: ijackson

library/std/src/process.rs

@@ -170,6 +170,7 @@ use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
 ///
 /// [`wait`]: Child::wait
 #[stable(feature = "process", since = "1.0.0")]
+#[must_use = "this Child should probably be `wait`ed, or `status` used instead of `spawn`"]
 pub struct Child {
     handle: imp::Process,