Add BaseSpectrum support to equalize_channels

Author: tsbinns

mne/channels/channels.py

@@ -148,21 +148,24 @@ def equalize_channels(instances, copy=True, verbose=None):
     from ..forward import Forward
     from ..io import BaseRaw
     from ..time_frequency import BaseTFR, CrossSpectralDensity
+    from ..time_frequency.spectrum import BaseSpectrum
 
     # Instances need to have a `ch_names` attribute and a `pick_channels`
     # method that supports `ordered=True`.
     allowed_types = (
         BaseRaw,
         BaseEpochs,
         Evoked,
+        BaseSpectrum,
         BaseTFR,
         Forward,
         Covariance,
         CrossSpectralDensity,
         Info,
     )
     allowed_types_str = (
-        "Raw, Epochs, Evoked, TFR, Forward, Covariance, CrossSpectralDensity or Info"
+        "Raw, Epochs, Evoked, Spectrum, TFR, Forward, Covariance, CrossSpectralDensity "
+        "or Info"
     )
     for inst in instances:
         _validate_type(