[Backport] Magento_Sales integration tests: fix invoice_list fixture var tags

[ronak2ram]

Original Pull Request

#16350

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 @ronak2ram. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me {$VERSION} instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[magento-engcom-team]

Hi @ronak2ram. Thank you for your contribution.
We will aim to release these changes as part of 2.2.6.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.