Ignore errors when cleaning up old wpt virtualenv

Differential Revision: https://phabricator.services.mozilla.com/D197578

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1871425
gecko-commit: f3216cc886f4cb5dc3617187c331a065c256cb2a
gecko-reviewers: ahal
diff --git a/tools/wpt/virtualenv.py b/tools/wpt/virtualenv.py
index 742f572..f1fad73 100644
--- a/tools/wpt/virtualenv.py
+++ b/tools/wpt/virtualenv.py
@@ -46,7 +46,7 @@
 
     def create(self):
         if os.path.exists(self.path):
-            shutil.rmtree(self.path)
+            shutil.rmtree(self.path, ignore_errors=True)
             self._working_set = None
         call(*self.virtualenv, self.path)