patch 8.2.3512: timestamp test fails on some systems

Problem:    Timestamp test fails on some systems.
Solution:   Sleep for a short while.
diff --git a/src/testdir/test_stat.vim b/src/testdir/test_stat.vim
index b565281..38ced6d 100644
--- a/src/testdir/test_stat.vim
+++ b/src/testdir/test_stat.vim
@@ -103,6 +103,7 @@
 
   w!
   silent !echo bar > Xautoread
+  sleep 10m
   checktime
 
   call assert_equal('bar', trim(getline(1)))