Fixes Rubocop Migration/AddLimitToTextColumns failures

What does this MR do and why?

Solves: #388821 (closed)

It circuit-breaks array_column?(node) method when the node is not of the type RuboCop::AST::SymbolNode.

This rule is intend to work when adding a new array column in post-migrations.

Ex:

class AddNewArrayColumn < Gitlab::Database::Migration[2.1]
  def up
    add_column :my_column, :numbers, :integer, array: true, default: []
  end

  def down
    # no-op
  end
end

bin/bundle exec rubocop db/post_migrate/add_new_array_column.rb

C: Migration/SchemaAdditionMethodsNoPost: This method may not be used in post migrations. Please see documentation here: https://docs.gitlab.com/ee/development/migration_style_guide.html#choose-an-appropriate-migration-type

How to set up and validate locally

1. generate a new post-migration file:

   rails g post_deployment_migration TestRubocopMigration

2. change the migration's body to include:

   column = :partition_id
   
   define_batchable_model(:ci_build).where(column => 100)

3. execute rubocop

   bin/bundle exec rubocop db/post_migrate/migrationnumber_test_rubocop_migration.rb

4. In master this should raise and error
5. In 388821-rubocop-migration-addlimittotextcolumns-failures branch, this should not raise any error

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Related to #388821 (closed)