Change "time (s)" to "freq (Hz)" in raw.plot_psd_topo()

[virvw]

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import mne

fname = mne.datasets.sample.data_path() + '/MEG/sample/sample_audvis_raw.fif'
raw = mne.io.read_raw_fif(fname)
raw = mne.concatenate_raws([raw])
raw.save('test_raw.fif', overwrite=True)
raw_read = mne.io.read_raw_fif('test_raw.fif')  # this breaks

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