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_viminfo.vim b/src/testdir/test_viminfo.vim
index f168e15..0551ea1 100644
--- a/src/testdir/test_viminfo.vim
+++ b/src/testdir/test_viminfo.vim
@@ -301,7 +301,7 @@
   call test_settime(39)
   call histadd(':', "echo '39'")
   wviminfo Xviminfo
-  
+
   call histdel(':')
   rviminfo Xviminfo
   call assert_equal("echo '39'", histget(':', -1))
@@ -560,7 +560,7 @@
   sp Xviminfo
   call assert_equal('latin1', &fenc)
   close
-  
+
   call histdel(':')
   rviminfo Xviminfo
   call assert_equal("echo 'é'", histget(':', -1))