Fix race condition that results in missing Retry-After header

when rate limit exceeded.

Author: rouilj

roundup/rest.py

@@ -2090,6 +2090,7 @@ def dispatch(self, method, uri, input):
                         # to the client. We treat update as sole
                         # source of truth for exceeded rate limits.
                         retry_after = 1
+                        self.client.setHeader('Retry-After', '1')
 
                     msg = _("Api rate limits exceeded. Please wait: %s seconds.") % retry_after
                     output = self.error_obj(429, msg, source="ApiRateLimiter")