Fixed worker exit code vs exit code confusion

Author: boxed

mutmut/__main__.py

@@ -607,6 +607,7 @@ def register_pid(self, *, pid, key, estimated_time_of_tests):
     def register_result(self, *, pid, exit_code):
         assert self.key_by_pid[pid] in self.exit_code_by_key
         self.exit_code_by_key[self.key_by_pid[pid]] = (0xFF00 & exit_code) >> 8  # The high byte contains the exit code
+        self.exit_code_by_key[self.key_by_pid[pid]] = exit_code
         # TODO: maybe rate limit this? Saving on each result can slow down mutation testing a lot if the test run is fast.
         del self.key_by_pid[pid]
         del self.start_time_by_pid[pid]