patch 9.0.1257: code style is not check in test scripts

Problem:    Code style is not check in test scripts.
Solution:   Add basic code style check for test files.
diff --git a/src/testdir/test_winbuf_close.vim b/src/testdir/test_winbuf_close.vim
index 17e31e4..5175c2c 100644
--- a/src/testdir/test_winbuf_close.vim
+++ b/src/testdir/test_winbuf_close.vim
@@ -219,7 +219,7 @@
   execute "normal \<c-w>b"
   let h = winheight(0)
   let w = win_getid()
-  new 
+  new
   q
   call assert_equal(h, winheight(0), "Window height does not match eight before opening and closing another window")
   call assert_equal(w, win_getid(), "Did not return to original window after opening and closing a window")