patch 8.2.2623: some tests fail when run as root

Problem:    Some tests fail when run as root.
Solution:   Use CheckNotRoot.
diff --git a/src/testdir/test_excmd.vim b/src/testdir/test_excmd.vim
index 0170a9f..cbeedfa 100644
--- a/src/testdir/test_excmd.vim
+++ b/src/testdir/test_excmd.vim
@@ -350,13 +350,6 @@
     call assert_fails('redir > Xdir', 'E17:')
     call delete('Xdir', 'd')
   endif
-  if !has('bsd')
-    " Redirecting to a read-only file
-    call writefile([], 'Xfile')
-    call setfperm('Xfile', 'r--r--r--')
-    call assert_fails('redir! > Xfile', 'E190:')
-    call delete('Xfile')
-  endif
 
   " Test for redirecting to a register
   redir @q> | echon 'clean ' | redir END
@@ -369,6 +362,17 @@
   call assert_equal('blue sky', color)
 endfunc
 
+func Test_redir_cmd_readonly()
+  CheckNotRoot
+  CheckNotBSD
+
+  " Redirecting to a read-only file
+  call writefile([], 'Xfile')
+  call setfperm('Xfile', 'r--r--r--')
+  call assert_fails('redir! > Xfile', 'E190:')
+  call delete('Xfile')
+endfunc
+
 " Test for the :filetype command
 func Test_filetype_cmd()
   call assert_fails('filetype abc', 'E475:')