Magento_Sales integration tests: fix invoice_list fixture var tags

[evktalo]

Description

In the invoice_list fixture for Magento/Sales integration tests, the var tags changed in this pull request refer to non-existing variables and the other has a wrong type.

Fixed Issues (if relevant)

None.

Manual testing scenarios

1. Open the fixture file in PHPStorm
2. Check if usage of the variables in the var tags can be found
3. Check if the type of the variable is shown correctly

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 @orlangur, thank you for the review.
ENGCOM-2115 has been created to process this Pull Request

[magento-engcom-team]

@evktalo thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[orlangur]

Hi @evktalo! Any contributions should be applied to 2.2-develop first, please create corresponding 2.2 PRs for both of your PRs.

[magento-engcom-team]

Hi @evktalo. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.3.0 release.