Unable to modify the node of a combined assc. when a child of that assc. is combined.

[dhnaranjo]

Describe the bug

When using nested combine you are unable to modify the node of the first level of nesting. This ones is best explained by the script, but there's a fair amount of setup. The juicy part:

arel.combine(bbb: :ccc).node(:bbb) { _1.select(:id) }
# => wrong argument type Symbol (expected Array)

To Reproduce

require "rom"
require "rom-sql"
require "dry-types"
require "sqlite3"

rom = ROM.container(:sql, 'sqlite::memory') do |config|
  config.default.create_table(:cccs) do
    primary_key :id
  end
  config.default.create_table(:bbbs) do
    primary_key :id
    Integer :ccc_id
  end
  config.default.create_table(:aaas) do
    primary_key :id
    Integer :bbb_id
  end
  config.relation(:cccs) do
    schema do
      attribute :id, Dry::Types["integer"]
      primary_key :id
    end
  end
  config.relation(:bbbs) do
    schema do
      attribute :id, Dry::Types["integer"]
      primary_key :id
      attribute :ccc_id, Dry::Types["integer"]

      associations do
        belongs_to :ccc
      end
    end
  end
  config.relation(:aaas) do
    schema do
      attribute :id, Dry::Types["integer"]
      primary_key :id
      attribute :bbb_id, Dry::Types["integer"]

      associations do
        belongs_to :bbb
      end
    end
  end
end

arel = rom.relations[:aaas]
brel = rom.relations[:bbbs]
crel = rom.relations[:cccs]

brel.changeset(:create, id: 1).commit
crel.changeset(:create, id: 1).commit
arel.changeset(:create, bbb_id: 1, ccc_id: 1).commit

arel.combine(bbb: :ccc).node(:bbb) { _1.select(:id) }
# => wrong argument type Symbol (expected Array)

Expected behavior

I can work with the first level node.

My environment

• Affects my production application: no
• Ruby version: 3.1.1
• OS: M1 Mac