USAGOV-2216 add weitzman/drupal-test-traits dependency

[gchi25]

Jira Task

https://cm-jira.usa.gov/browse/USAGOV-2216

Description

Adds weitzman/drupal-test-traits dependency.
This ensures that PHPStan can discover the ExistingSiteBase class.

Type of Changes

• New Feature
• Bugfix
• Frontend (Twig, Sass, JS)
  • Add screenshot showing what it should look like
• Drupal Config (requires "drush cim")
• New Modules (requires rebuild)
• Documentation
• Infrastructure
  • CMS
  • WAF
  • WWW
  • Egress
  • Tools
  • Cron
• Other

Testing Instructions

Change Requirements

• Requires New Documentation (Link: {})
• Requires New Config
• Requires New Content

Validation Steps

• Test instruction 1
• Test instruction 2
• Test instruction 3

Security Review

• Adds/updates software (including a library or Drupal module)
• Communication with external service
• Changes permissions or workflow
• Requires SSPP updates

Reviewer Reminders

• Reviewed code changes
• Reviewed functionality
• Security review complete or not required

Post PR Approval Instructions

Follow these steps as soon as you merge the new changes.

1. Go to the USAGov Circle CI project.
2. Find the commit of this pull request.
3. Build and deploy the changes.
4. Update the Jira ticket by changing the ticket status to Review in Test and add a comment. State whether the change is already visible on cms-dev.usa.gov and beta-dev.usa.gov, or if the deployment is still in process.

[akf]

It works for me and I'm approving this, but since it's a Draft PR I won't merge it.

Did you mean to to also remove web/modules/custom/usagov_benefit_finder from the excludePaths section of phpstan.neon? I think that would be reasonable.