PHPUnit 9 Shift

[drysius]

This pull request contains changes for upgrading to PHPUnit 9 automated by the PHPUnit 9 Shift.

Before merging, you need to:

• Checkout the shift-89632 branch
• Review all pull request comments for additional changes
• Run composer update (if the scripts fail, add --no-scripts)
• Run your tests suite: vendor/bin/phpunit

If there were changes you felt could have been automated, please reply to the follow-up email with your feedback or on Twitter.