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)

src/testdir/test_autoload.vim

@@ -22,3 +22,5 @@ func Test_autoload_vim9script()
   call assert_equal('some', auto9#getsome())
   call assert_equal(49, auto9#add42(7))
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab