Add run step to patch the Lua 5.1 sources

[natecraddock]

I maintain a version of Lua 5.1 that has a patch for security https://github.com/natecraddock/lua

I think it would be better to use the Lua 5.1 tarball from lua.org and use the Zig build system to apply the patch. This would be better for transparency and trust.

The patch is small and it should be simple to write a script to apply the patch to the file.