luarocks: add test for [email protected] and luajit

[carlocab]

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Follows up #65993

This PR commits a test-only change, so probably doesn't need to pass CI (though it does on 11.0 and 10.14. Catalina nodes are being weird atm).

[carlocab]

10.15 error:

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

[carlocab]

10.14 succeeds, but 10.15 build error:

==> brew uninstall --force lua [email protected] [email protected]
Error: No available formula with the name "vv".
Error: Process completed with exit code 1.

I get this error even if I just give luarocks a revision bump (826764a): https://github.com/Homebrew/homebrew-core/runs/1504433319

NoSome idea of what's going on:

❯ brew uses --include-build --include-test --recursive luarocks
corsixth        lmod            neovim          sile            vis             vv
❯ brew info vv
vv: 2.3.0
https://github.com/vv-vim/vv
Not installed
From: https://github.com/Homebrew/homebrew-cask/blob/HEAD/Casks/vv.rb
...

CI wants to test vv because it's reported as depending on luarocks through neovim. However, vv is a cask, so won't work with brew install --formula. See #66268.

[BrewTestBot]

@fxcoudert has triggered a merge.