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_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 1452e4d..fc7e8cb 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -2149,7 +2149,7 @@
 
 func Test_ins_complete_end_of_line()
   " this was reading past the end of the line
-  new  
+  new
   norm 8o€ý 
   sil! norm o