fix(rocks): add lib64 plugin directory to package.cpath

[carbon-steel]

Description

package.cpath is missing the lib64 directory for plugins that have luarocks dependencies.

Context

I found this issue when I was working on my new Neovim plugin on my Fedora 39 machine. I added the luasockets dependency to rockspec file in my plugin like so:

rockspec_format = "3.0"
package = "typeracer.nvim"
version = "scm-1"
source = {
	url = "git+https://github.com/carbon-steel/typeracer.nvim",
}
dependencies = {
	"luasocket",
}
test_dependencies = {
	"nlua",
}
build = {
	type = "builtin",
	copy_directories = {},
}

I found that the dynamic libraries from the luasockets dependency were installed like so: /home/username/.local/share/nvim/lazy-rocks/typeracer.nvim/lib64/lua/5.1/socket/core.so. However, the only entry related to my plugin typeracer.nvim was: /home/glyph/.local/share/nvim/lazy-rocks/typeracer.nvim/lib/lua/5.1/?.so. The issue is that we only have the plugin's lib directory in package.cpath and not lib64.

I looked through lazy.nvim's code and I think adding the lib64 directory should fix the issue. I don't know if we also want to worry about lib32 as well, but so far, this change works for me.

[carbon-steel]

I'm not sure how to fix the failing PR title job :/

[folke]

ty!