FED-1161 Unpin mockito, fix CI

[greglittlefield-wf]

Motivation

In https://github.com/Workiva/react-dart/pull/355, we noticed that CI was failing on the beta channel (Dart 3) since this package is not yet null safe, and on the stable channel (2.19) due to https://github.com/dart-lang/sdk/issues/51128.

In fixing and updating CI, I realized that mockito was pinned unnecessarily, since there were no dependencies preventing us from getting on the latest, and CI just needed to be updated to not run on older SDKs (2.13) in which it wouldn't resolve.

Solution

• Unpin mockito
• Update SDK versions used in CI
  • Before: 2.13.4, stable (2.19), beta (3)
  • After: 2.18.7, stable (2.19)
• Format code using 2.18.7

QA instructions

• CI passes

[aviary2-wf]

Security Insights

No security relevant content was detected by automated scans.

Action Items

• Review PR for security impact; comment "security review required" if needed or unsure

• Verify aviary.yaml coverage of security relevant code

  Questions or Comments? Reach out on Slack: #support-infosec.

[robbecker-wf]

QA+1 CI Passes now for all stages

[greglittlefield-wf]

@Workiva/release-management-p