fix: clear kernel instance so the global/singleton is not reused again

Author: maartenbreddels

ipykernel/kernelapp.py

@@ -568,7 +568,7 @@ def new_event_loop(self):
                     # TODO: we might want to pass the same arguments, except the file
                     # NOTE: we actually start a new kernel, but once this works
                     # we can actually think about reusing the kernel object
-                    self.initialize(argv=['-f', 'conn_fork.json', '--debug'])
+                    self.kernel_class.clear_instance()
                     self.start()
                     pass
                 else: