Fix staticcheck errors on Windows.

pkg/cli/term/read_rune.go

@@ -1,3 +1,5 @@
+//go:build !windows && !plan9
+
 package term
 
 import (

pkg/cli/term/reader_windows.go

@@ -71,9 +71,9 @@ func (r *reader) Close() {
 	if err != nil {
 		log.Println("SetEvent:", err)
 	}
+	r.mutex.Lock()
 	//lint:ignore SA2001 We only lock the mutex to make sure that ReadEvent has
 	//exited, so we unlock it immediately.
-	r.mutex.Lock()
 	r.mutex.Unlock()
 	err = windows.CloseHandle(r.stopEvent)
 	if err != nil {

pkg/testutil/umask.go

@@ -3,5 +3,5 @@ package testutil
 // Umask sets the umask for the duration of the test, and restores it afterwards.
 func Umask(c Cleanuper, m int) {
 	save := umask(m)
-	c.Cleanup(func() { umask(save) })
+	c.Cleanup(func() { _ = umask(save) })
 }