doc: fix rendering typo rst docstr (#13301)

Author: sappelhoff

mne/time_frequency/spectrum.py

@@ -1380,7 +1380,7 @@ class EpochsSpectrum(BaseSpectrum, GetEpochsMixin):
         Frequencies at which the amplitude, power, or fourier coefficients
         have been computed.
     %(info_not_none)s
-    method : ``'welch'``| ``'multitaper'``
+    method : ``'welch'`` | ``'multitaper'``
         The method used to compute the spectrum.
     weights : array | None
         The weights for each taper. Only present if spectra computed with