patch 8.1.2133: some tests fail when run as root

Problem:    Some tests fail when run as root.
Solution:   Add CheckNotRoot and use it. (James McCoy, closes #5020)
diff --git a/src/testdir/test_viminfo.vim b/src/testdir/test_viminfo.vim
index 7ea9f78..a9dc8fd 100644
--- a/src/testdir/test_viminfo.vim
+++ b/src/testdir/test_viminfo.vim
@@ -736,6 +736,7 @@
 " Test for an unwritable and unreadble 'viminfo' file
 func Test_viminfo_perm()
   CheckUnix
+  CheckNotRoot
   call writefile([''], 'Xviminfo')
   call setfperm('Xviminfo', 'r-x------')
   call assert_fails('wviminfo Xviminfo', 'E137:')