@tom-tan A test may use a specific version if there is no other way.  Elixir does already.

I am not sure in this case.  The repository may be convenient, but I do not like it.  It's not an official repository and the website is unhelpful (to say the best).  There is no information about the kind of packages included (i.e. are these official builds, are they compatible, etc.), and no guarantee of continued maintenance.