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_memory_usage.vim

@@ -162,3 +162,5 @@ func Test_memory_func_capture_lvars()
   call vim.stop()
   call delete(testfile)
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab