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_indent.vim b/src/testdir/test_indent.vim
index 290855e..96e9d23 100644
--- a/src/testdir/test_indent.vim
+++ b/src/testdir/test_indent.vim
@@ -175,7 +175,7 @@
 endfunc
 
 func Test_indent_func_with_gq()
-  
+
   function GetTeXIndent()
     " Sample indent expression for TeX files
     let lnum = prevnonblank(v:lnum - 1)
@@ -186,7 +186,7 @@
     let line = getline(lnum)
     let ind = indent(lnum)
     " Add a 'shiftwidth' after beginning of environments.
-    if line =~ '\\begin{center}' 
+    if line =~ '\\begin{center}'
       let ind = ind + shiftwidth()
     endif
     return ind
@@ -248,7 +248,7 @@
 
   bwipe!
   delmark ab
-  delfunction GetTeXIndent 
+  delfunction GetTeXIndent
 endfu
 
 func Test_formatting_keeps_first_line_indent()