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_timers.vim b/src/testdir/test_timers.vim
index 8e6d7f9..fe80bb9 100644
--- a/src/testdir/test_timers.vim
+++ b/src/testdir/test_timers.vim
@@ -393,7 +393,7 @@
 " vgetc().
 func Test_nocatch_timer_garbage_collect()
   " FIXME: why does this fail only on MacOS M1?
-  try 
+  try
     CheckNotMacM1
   catch /Skipped/
     let g:skipped_reason = v:exception