Add FXIOS-15434 [Newsfeed Categories] Merino categories test data

[Foxbolts]

📜 Tickets

Jira ticket
Github issue

💡 Description

• Add mock data for Merino categories
  • Mock data is used for tests and to display categories on the homepage in developer builds

📝 Checklist

• I filled in the ticket numbers and a description of my work
• I updated the PR name to follow our PR naming guidelines
• I ensured unit tests pass and wrote tests for new code
• If working on UI, I checked and implemented accessibility (Dynamic Text and VoiceOver)
• If adding telemetry, I read the data stewardship requirements and will request a data review
• If adding or modifying strings, I read the guidelines and will request a string review from l10n
• If needed, I updated documentation and added comments to complex code

[mobiletest-ci-bot]

	Messages
📖	Project coverage: 41.23%

💪 Quality guardian

1 tests files modified. You're a champion of test coverage! 🚀

🧹 Tidy commit

Just 3 file(s) touched. Thanks for keeping it clean and review-friendly!

✅ New file code coverage

No new file detected so code coverage gate wasn't ran.

Client.app: Coverage: 39.57

File	Coverage
MerinoProvider.swift	89.22%	✅
MerinoTestData.swift	99.5%	✅

Generated by 🚫 Danger Swift against 3c233e5

[adudenamedruby]

LGTM

[github-actions]

🚀 PR merged to main, targeting version: 150.1