Bind ignored results.

std::io::Error implements Drop in some configurations. A value that
implements Drop will be dropped immediately when not bound (and _ does
not bind). This is asymptomatic in this case but we want to deny this
behavior globally because it has very surprising behavior when the
"unused" value is a lock.

Bug: 281730184
Test: mm
Change-Id: I325f7bb1ca8eb74f56fbb3926e4e79e833a265a4
diff --git a/authfs/service/src/authfs.rs b/authfs/service/src/authfs.rs
index 3e8e0e0..cfd5766 100644
--- a/authfs/service/src/authfs.rs
+++ b/authfs/service/src/authfs.rs
@@ -176,7 +176,7 @@
             bail!("Child has exited: {}", exit_status);
         }
         if start_time.elapsed() > AUTHFS_SETUP_TIMEOUT_SEC {
-            let _ = child.kill();
+            let _ignored = child.kill();
             bail!("Time out mounting authfs");
         }
         sleep(AUTHFS_SETUP_POLL_INTERVAL_MS);