matplotlib version 3.8 results in test failure

[ldXiao]

Describe the bug
Using matplotlib 3.8 results in runtime error in calculations.py

To Reproduce
Steps to reproduce the behavior:

1. uninstall matplotlib old version and install matplotlib stable version
2. run make tests

error message

=================== short test summary info ==================== 
FAILED aat/tests/strategy/test_offline_calculations.py::TestOfflineCalculations::test_calculations - AttributeError: 'GrouperView' object has no attribute 'join'

with some simple debug, we can trace to line 335 of aat/tests/strategy/test_offline_calculations.py:

...python
        # join all but last on x axis
        for ax in axes[:-1]:
            axes[0].get_shared_x_axes().join(axes[0], ax)
...

where newer version of matplotlib has modified the method get_shared_x_axes() to return cbook.GrouperView object which does not have an attribute join

We can either restrict the maximum version number of matplotlib or modify aat code to make it compatible