Update allowlist of methods to ignore for false positives

[smcabrera]

Created as a draft for now so I can come back and add some examples to reproduce the issue I'm having and give some more context.

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Back in September of last year @pyromaniac reported an issue with false positives for the Rails/HttpPositionalArguments cop when routes are defined within specs. That issue was subsequently fixed by #533. However there was one piece that was not fully addressed.

While the following code will no longer produce a false positive:

# frozen_string_literal: true

RSpec.describe FooController do
  before do
    routes do
      get :list, on: :collection
    end

    Rails.application.routes.draw do
      get :list, on: :collection
    end
  end

  specify do
    get :list, filter: 42
  end
end

We'll still get a false positive when the `append` method is invoked

Rails.application.routes.append do
  get 'some-fake-endpoint', on: :collection

Adding to the list of methods to ignore for false positives seems to successfully address this issue. The change is very small.

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• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
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• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
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