Address a type-conversion noted during doc builds #3623
                
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Doc builds show the following output:
This is addressed by upgrading
source_suffixto a dict inconf.py.Note
As reported in #3622, the scheduled doc builds are currently failing in
main. I expect the doc builds to fail here, as well, but it is not related. This PR is simply a minor update based on output I observed while investigating #3622.tox -e fix)docs/changelogfolder