patch 8.2.1432: various inconsistencies in test files

Problem:    Various inconsistencies in test files.
Solution:   Add modelines where they were missing.  Use Check commands instead
            of silently skipping over tests.  Adjust indents and comments.
            (Ken Takata, closes #6695)
diff --git a/src/testdir/test_global.vim b/src/testdir/test_global.vim
index 1e79ed1..ee4808c 100644
--- a/src/testdir/test_global.vim
+++ b/src/testdir/test_global.vim
@@ -1,3 +1,5 @@
+" Test for :global and :vglobal
+
 source check.vim
 
 func Test_yank_put_clipboard()