Fix warnings test CI

[bhazelton]

Description

Filter a warning caused by an interaction between pytest-cov and pytest-xdist that is breaking our warnings test CI.

Motivation and Context

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Documentation change (documentation changes only)
• [ ] Version change
• [x] Build or continuous integration change

Checklist:

• [x] I have read the contribution guide.
• [x] My code follows the code style of this project.

Build or continuous integration change checklist:

• [ ] If required or optional dependencies have changed (including version numbers), I have updated the readme to reflect this.
• [ ] If this is a new CI setup, I have added the associated badge to the readme and to references/make_index.py (if appropriate).