fix(core): validate non-string plugin

[Lilja]

Description

plugin[1] is assumed to be a string in this case. I did not add a proper plugin:

return {
  { 
    dev = {
      path = "/Users/lilja/open-source/telescope.nvim"
    } 
  }
}

Old error:

Error detected while processing /Users/lilja/dotfiles/nvim/init.lua:
Failed to load `plugins.telescope`

...al/share/nvim/lazy/lazy.nvim/lua/lazy/core/fragments.lua:109: attempt to call method 'find' (a nil value)

New error:

Error detected while processing /Users/lilja/dotfiles/nvim/init.lua:
Invalid plugin spec { {
    dev = {
      path = "/Users/lilja/open-source/telescope.nvim"
    }
  },
  config = <function 1>,
  dependencies = { "nvim-lua/plenary.nvim", "smartpde/telescope-recent-files", "camgraff/telescope-tmux.nvim", "KadoBOT/nvim-spotify", "natecraddock/telescope-zf-native.nvim", "nvim-telescope/telescope-file-browse
r.nvim", { "Lilja/telescope-swap-files" } }
}

[github-actions]

This PR is stale because it has been open 30 days with no activity.

[github-actions]

This PR is stale because it has been open 30 days with no activity.