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.

src/testdir/test_normal.vim

@@ -2209,7 +2209,7 @@ func Test_normal29_brace()
     a character like this:
     .NH
     End of text here
-  
+
   [DATA]
   call assert_equal(expected, getline(1, '$'))