facilitate running the testuite in a sandbox

[teto]

hi,

I managed to run the testsuite (minus a few tests) for my linux distribution nixos see NixOS/nixpkgs#483694.

The current orgmode test procedure setups the environment (install treesitter grammars and downloads plenary) before running the tests and it's not possible to run separately both. Which is an issue for nix (but certainly other distributions as well) where the build occurs in a sandbox without internet access.

It would be nice to differente between the two so that I can run a make test-with-environment-prepared instead of

      nvim --headless -i NONE \
        -u test/minimal_init.vim --cmd "set rtp+=${vimPlugins.plenary-nvim}" \
        -c "PlenaryBustedDirectory tests { sequential = true, minimal_init = './tests/minimal_init.lua' }"