[DOC, CI] Fix paths in examples for PosixPath

[adam2392]

PR Description

CI is failing because data_path() from MNE-Python used to return str, now it returns PosixPath.

Merge checklist

Maintainer, please confirm the following before merging:

• [ ] All comments resolved
• [ ] This is not your own PR
• [ ] All CIs are happy
• [ ] PR title starts with [MRG]
• [ ] whats_new.rst is updated
• [ ] PR description includes phrase "closes <#issue-number>"

[adam2392]

@larsoner any chance you know why the error is occurring in viz? I tried looking at MNE-Python and changing the requirements, but that doesn't seem to fix the issue. Seems like a backend issue to me(?)

________________________ test_plot_connectivity_circle ________________________
mne_connectivity\viz\tests\test_circle.py:82: in test_plot_connectivity_circle
    plot_connectivity_circle(con, label_names, n_lines=300,
mne_connectivity\viz\circle.py:144: in plot_connectivity_circle
    return _plot_connectivity_circle(
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\mne\viz\circle.py:194: in _plot_connectivity_circle
    fig = plt.figure(figsize=(8, 8), facecolor=facecolor)
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\_api\deprecation.py:454: in wrapper
    return func(*args, **kwargs)
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\pyplot.py:771: in figure
    manager = new_figure_manager(
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\pyplot.py:347: in new_figure_manager
    return _get_backend_mod().new_figure_manager(*args, **kwargs)
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\backend_bases.py:3504: in new_figure_manager
    fig = fig_cls(*args, **kwargs)
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\_api\deprecation.py:454: in wrapper
    return func(*args, **kwargs)
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\figure.py:2406: in __init__
    super().__init__(**kwargs)
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\figure.py:164: in __init__
    super().__init__()
C:\hostedtoolcache\windows\Python\3.9.13\x64\lib\site-packages\matplotlib\artist.py:171: in __init__
    self._callbacks = cbook.CallbackRegistry(signals=["pchanged"])
E   TypeError: __init__() got an unexpected keyword argument 'signals'

[drammock]

probably this: https://github.com/matplotlib/matplotlib/pull/21238

can you follow up with the MPL folks?