update test expectations for an upcoming version of package:args

[devoncarew]

• update test expectations for an upcoming version of package:args

A follow-up to #3901 to address one more test expectation. If we don't want to relax the way PackageWarningCounter works, we could just skip this test for a bit, until the next version of args is out.

---

• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

Contribution guidelines:

• See our contributor guide for general expectations for PRs.
• Larger or significant changes should be discussed in an issue before creating a PR.
• Contributions to our repos should follow the Dart style guide and use dart format.
• Most changes should add an entry to the changelog and may need to rev the pubspec package version.
• Changes to packages require corresponding tests.

Note that many Dart repos have a weekly cadence for reviewing PRs - please allow for some latency before initial review feedback.