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_method.vim b/src/testdir/test_method.vim
index 29734e0..2ca66fd 100644
--- a/src/testdir/test_method.vim
+++ b/src/testdir/test_method.vim
@@ -127,7 +127,7 @@
 
 func Test_method_syntax()
   eval [1, 2, 3]  ->sort( )
-  eval [1, 2, 3]  
+  eval [1, 2, 3]
 	\ ->sort(
 	\ )
   eval [1, 2, 3]->sort()