Refactor FXIOS-12796 [Swift 6 Migration] Fix Sendable warnings in CreditCardSettingsViewModel and CreditCardInputViewModel

[ih-codes]

📜 Tickets

Jira ticket
Github issue

Fix Sendable warnings in CreditCardSettingsViewModel and CreditCardInputViewModel

📝 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: 38.26%

🧹 Tidy commit

Just 2 file(s) touched. Thanks for keeping it clean and review-friendly!

✅ Per-file coverage

All changed files meet the threshold of 35.0%.

Client.app: Coverage: 37.12

File	Coverage
CreditCardSettingsViewModel.swift	46.38%	⚠️
CreditCardInputViewModel.swift	62.01%	✅

Generated by 🚫 Danger Swift against d670f5e