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_vim9_disassemble.vim b/src/testdir/test_vim9_disassemble.vim
index e47e013..1433bb7 100644
--- a/src/testdir/test_vim9_disassemble.vim
+++ b/src/testdir/test_vim9_disassemble.vim
@@ -2085,7 +2085,7 @@
         '8 COND2BOOL\_s*' ..
         '9 STORE $3\_s*' ..
         'return name\_s*' ..
-        '\d\+ LOAD $3\_s*' ..   
+        '\d\+ LOAD $3\_s*' ..
         '\d\+ RETURN',
         instr)
   assert_equal(true, InvertBool())