Magento_Sales integration tests: Fix addresses in order_list fixture

[evktalo]

Description

Addresses are broken in the order_list.php integration test fixture.

Instead of setting billing address twice, set both billing address and shipping address.
Reset $billingAddress and $shippingAddress variables with newly created Address objects. Otherwise trying to access the order's address data gives an error. (e.g. 'Call to a member function on null' when trying to use $order->getBillingAddress()->getFirstname())

Additionally, improve code style slightly.

I don't think this affects the present integration tests that use this fixture, but when you try to use this fixture in a test that does use the addresses, it will not work.

Fixed Issues (if relevant)

None.

Manual testing scenarios

1. Create an integration test that uses order_list fixture
2. Create order in the test
3. Call $order->getShipppingAddress()->getFirstname()

Without the fix, you will get a 'Call to a member function on null' error.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @evktalo. Thank you for your contribution
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[magento-engcom-team]

Hi @dmanners, thank you for the review.
ENGCOM-2252 has been created to process this Pull Request

[magento-engcom-team]

Hi @evktalo. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.