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_balloon_gui.vim b/src/testdir/test_balloon_gui.vim
index 70a88f3..d01114c 100644
--- a/src/testdir/test_balloon_gui.vim
+++ b/src/testdir/test_balloon_gui.vim
@@ -17,3 +17,5 @@
   sleep 10m
   call balloon_show('')
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab