Show regrtest env changed warn on Windows buildbot

Issue #27829: don't pass --quiet option to regrtest to see
"Warning -- xxx was modified by ..." warnings.

Tools/buildbot/test.bat

@@ -3,7 +3,7 @@ rem Used by the buildbot "test" step.
 setlocal
 
 set here=%~dp0
-set rt_opts=-q -d
+set rt_opts=-d
 set regrtest_args=-j1
 
 :CheckOpts