Allow datetime or str in test_sequential_control_messages

[ianthomas23]

Fixes #1218.

test_sequential_control_messages added in #1210 compares two datetimes returned in execute_reply messages. Some downstream libraries (ipyparallel) keep them as strings for performance reasons, so here allow this test to accept datetime or strings, otherwise this test is testing the return types rather than the intended sequence of control messages.

Once this passes CI here and is merged, we will need to check that IPythons CI also passes before we can be sure that it is fully fixed.

[ianthomas23]

Failures here are the same as in the last scheduled CI run https://github.com/ipython/ipykernel/actions/runs/8134006247

[blink1073]

This failure on Windows looks relevant:

FAILED tests/test_kernel.py::test_sequential_control_messages - assert datetime.datetime(2024, 3, 4, 12, 12, 34, 411229, tzinfo=datetime.timezone.utc) > datetime.datetime(2024, 3, 4, 12, 12, 34, 411229, tzinfo=tzutc())

[ianthomas23]

Windows tests are passing now.

[blink1073]

Thank you!