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_ga.vim b/src/testdir/test_ga.vim
index ce31edf..a0050fa 100644
--- a/src/testdir/test_ga.vim
+++ b/src/testdir/test_ga.vim
@@ -1,4 +1,5 @@
 " Test ga normal command, and :ascii Ex command.
+
 func Do_ga(c)
   call setline(1, a:c)
   let l:a = execute("norm 1goga")