[MRG] Fixed group_by titles in evoked_plot. (#10618)

* Fixed group_by titles in evoked_plot.

* added contribution info

doc/changes/latest.inc

@@ -98,6 +98,8 @@ Bugs
 
 - Fix issue with saving epochs once :func:`~mne.preprocessing.compute_current_source_density` has been used if a rejection threshold was used first (:gh:`10619` by `Alex Rockhill`_ and `Richard Höchenberger`_)
 
+- Fix bug in :func:`mne.viz.plot_evoked_image` that would cause incorrect sub-titles when using ``group_by`` (:gh:`10618` by `Reza Shoorangiz`_)
+
 API and behavior changes
 ~~~~~~~~~~~~~~~~~~~~~~~~
 - When creating BEM surfaces via :func:`mne.bem.make_watershed_bem` and :func:`mne.bem.make_flash_bem`, the ``copy`` parameter now defaults to ``True``. This means that instead of creating symbolic links inside the FreeSurfer subject's ``bem`` folder, we now create "actual" files. This should avoid troubles when sharing files across different operating systems and file systems (:gh:`10531` by `Richard Höchenberger`_)

mne/viz/evoked.py

@@ -236,10 +236,10 @@ def _plot_evoked(evoked, picks, exclude, unit, show, ylim, proj, xlim, hline,
                                  "found in `axes`")
             ax = axes[sel]
             # the unwieldy dict comp below defaults the title to the sel
-            titles = ({channel_type(evoked.info, idx): sel
-                       for idx in group_by[sel]} if titles is None else titles)
+            title = ({channel_type(evoked.info, idx): sel
+                      for idx in group_by[sel]} if titles is None else titles)
             _plot_evoked(evoked, group_by[sel], exclude, unit, show, ylim,
-                         proj, xlim, hline, units, scalings, titles,
+                         proj, xlim, hline, units, scalings, title,
                          ax, plot_type, cmap=cmap, gfp=gfp,
                          window_title=window_title,
                          selectable=selectable, noise_cov=noise_cov,