This looks easy, but code comments make me wonder whether this is a good change to be making. The code to insert display-authors=9 is a special case, inserted so that "et al. " would not hide only one author (from code comments: "Better display an author's name than 'et al' when the et al only hides 1 author!"). I am not sure whether the reasoning that led to this special case is still valid. Commented here to ask: https://en.wikipedia.org/wiki/User_talk:Citation_bot#.7Cdisplay-authors.3D9_no_longer_necessary_for_exactly_nine_authors

Perhaps the {{cite journal}} template on testwiki is out of date? https://test.wikipedia.org/w/index.php?title=User:Fhocutt_%28WMF%29/Citation_bot_test&oldid=244444 shows et al. still present, but looking at the same citation here https://en.wikipedia.org/w/index.php?title=Penicillium_pinophilum&type=revision&diff=682189717&oldid=682189517 shows all authors.

Related branch/commit on github: https://github.com/fhocutt/citation-bot/commit/40968c75f4f3fe335cddc2fdd6cdbccbda268b4f

Answer from Jonesey95:

The CS1 citation module (and its predecessor code) that renders {{cite journal}} and similar templates used to display "et al." when exactly nine authors were listed, for reasons too boring to go into. The module no longer does that; it displays all authors unless |display-authors=x is used (where x is a number less than the number of authors in the cite template). So |display-authors=9 is redundant when there are exactly nine authors listed.

I've updated the CS1 module on testwiki to incorporate these changes.

Should be good to merge.

Merged and pulled onto Tool Labs.