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_autocmd.vim b/src/testdir/test_autocmd.vim
index 12fbcb7..8931678 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -269,8 +269,8 @@
   augroup testing
     au WinNew * call add(g:record, 'WinNew')
     au WinClosed * call add(g:record, 'WinClosed')
-    au WinEnter * call add(g:record, 'WinEnter') 
-    au WinLeave * call add(g:record, 'WinLeave') 
+    au WinEnter * call add(g:record, 'WinEnter')
+    au WinLeave * call add(g:record, 'WinLeave')
     au TabNew * call add(g:record, 'TabNew')
     au TabClosed * call add(g:record, 'TabClosed')
     au TabEnter * call add(g:record, 'TabEnter')
@@ -3406,7 +3406,7 @@
 
 func Test_Visual_doautoall_redraw()
   call setline(1, ['a', 'b'])
-  new 
+  new
   wincmd p
   call feedkeys("G\<C-V>", 'txn')
   autocmd User Explode ++once redraw
@@ -4121,7 +4121,7 @@
 
 func Test_autocmd_split_dummy()
   " Autocommand trying to split a window containing a dummy buffer.
-  auto BufReadPre * exe "sbuf " .. expand("<abuf>") 
+  auto BufReadPre * exe "sbuf " .. expand("<abuf>")
   " Avoid the "W11" prompt
   au FileChangedShell * let v:fcs_choice = 'reload'
   func Xautocmd_changelist()