quarto-web: move "Upload Index" workflow to Algolia V3

[cscheid]

Our workflow had been failing for about a month because the default Algolia Ruby library changed from v2 to v3 and it's a backwards-incompatible change.

I pinned our gem install algolia to 2.3.4, and that solved the immediate problem, but we need to move to v3 in the long run, from https://www.algolia.com/doc/libraries/ruby/v2/ to https://www.algolia.com/doc/libraries/ruby/v3/

I had hoped that the change was a one-liner, but alas, no: https://github.com/quarto-dev/quarto-web/actions/runs/10913293160/job/30289535056