Regression in multiple tests on macOS

There appears to be a regression that happened between 5.1.2 and 5.1.3. There are following tests are now failing on master:

* test_sys_path_profile_dir
* test_save_history - flaky?
* test_help_output - flaky?
* test_write_kernel_spec - flaky?
* test_ipython_start_kernel_userns
* test_display_hook_halts_send
* test_display_hook_return_calls_send
* test_display_publisher_creation
* test_publish
* test_thread_local_hooks
* test_unregister_hook

Bisecting this behaviour points to 846531b92198efc4db2a37bdadf4a037defcfd96 as the first bad commit. For some reason the problem is only seen on python 3.7 and not python 3.8.