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_window_id.vim b/src/testdir/test_window_id.vim
index 20465ae..396a49b 100644
--- a/src/testdir/test_window_id.vim
+++ b/src/testdir/test_window_id.vim
@@ -1,4 +1,5 @@
 " Test using the window ID.
+
 source check.vim
 
 func Test_win_getid()