OpenResty variant doesn't provide `lua` binary

[alerque]

Given that all the other variants including luajit have a lua symlink that can be used to run whatever version the CI matrix installed, it would be handy if the OpenResty variant did the same. Right now it has to be special cased to use luajit.

[alerque]

Any chance we can get this fixed? I doubt it's a complicated one, just a symlink somewhere. We're having to use v9 various places downstream to avoid issues related to this in v10. It would be nice to drop that nonsense.