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/setup.vim b/src/testdir/setup.vim
index 5b8f3f1..ca94bae 100644
--- a/src/testdir/setup.vim
+++ b/src/testdir/setup.vim
@@ -20,7 +20,7 @@
   let &packpath = &rtp
 endif
 
-" Only when the +eval feature is present. 
+" Only when the +eval feature is present.
 if 1
   " Make sure the .Xauthority file can be found after changing $HOME.
   if $XAUTHORITY == ''