Fix adding a new authentication source after selecting OAuth

[efy]

First contribution here, thought this would be a simple one.
Adds a comma.
Should fix issue #2802.

[codecov-io]

Codecov Report

Merging #2889 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2889   +/-   ##
=======================================
  Coverage   26.85%   26.85%           
=======================================
  Files          89       89           
  Lines       17607    17607           
=======================================
  Hits         4728     4728           
  Misses      12193    12193           
  Partials      686      686

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[lafriks]

LGTM

[ethantkoenig]

LGTM