LuaRocks for GitHub Actions (repository split)

All Lua actions were previously in the same repo but this is incompatible with the GitHub marketplace. Lua and LuaRocks are now split across two repositories:

• leafo/gh-actions-lua
• leafo/gh-actions-luarocks

Example:

- uses: leafo/gh-actions-lua@v2
- uses: leafo/gh-actions-luarocks@v2

- name: Install a pakage
  runs: luarocks install busted