patch 8.2.1340: some tests fail on Cirrus CI and/or with FreeBSD

Problem:    Some tests fail on Cirrus CI and/or with FreeBSD.
Solution:   Make 'backupskip' empty. Do not run tests as root. Check for
            directory when using viminfo. (Ozaki Kiichi, closes #6596)
diff --git a/src/testdir/test_viminfo.vim b/src/testdir/test_viminfo.vim
index 258b472..bc8afa0 100644
--- a/src/testdir/test_viminfo.vim
+++ b/src/testdir/test_viminfo.vim
@@ -807,7 +807,7 @@
 
   " Try to write the viminfo to a directory
   call mkdir('Xdir')
-  call assert_fails('wviminfo Xdir', 'E886:')
+  call assert_fails('wviminfo Xdir', 'E137:')
   call delete('Xdir', 'rf')
 endfunc