numpy binary incompatibility errors on merges to main (but not on PR CIs)

[drammock]

a bunch of tests are failing on azure on merges to main, with

ValueError: numpy.dtype size changed, may indicate binary incompatibility. Expected 96 from C header, got 88 from PyObject

(example: https://dev.azure.com/mne-tools/mne-connectivity/_build/results?buildId=32263&view=logs&j=1703785f-b0ab-5f68-8423-695936ace89c&t=050cef19-955a-57b1-eec9-ac4905d57bbe)

which is likely a case of "scipy/pandas/whatever was compiled against numpy 1.x but numpy 2.x is installed"

we should fix this.