patch 8.2.3534: autoread test is a bit flaky

Problem:    Autoread test is a bit flaky.
Solution:   Wait a brief moment before overwriting the file.
diff --git a/src/testdir/test_stat.vim b/src/testdir/test_stat.vim
index fa61c5c..de4a204 100644
--- a/src/testdir/test_stat.vim
+++ b/src/testdir/test_stat.vim
@@ -104,7 +104,8 @@
   setlocal autoread
   call setline(1, 'foo')
   w!
-  silent !echo bar > Xautoread
+  sleep 10m
+  call writefile(['bar'], 'Xautoread')
   sleep 10m
   checktime
   call assert_equal('bar', trim(getline(1)))