Code Review Bench PR #31547 - Refactor FXIOS-13122 [Swift 6] Remove @Sendable from closures marked as @MainActor

[tomerqodo]

Code Review Bench PR mozilla-mobile#31547

Original PR Title: Refactor FXIOS-13122 [Swift 6] Remove @sendable from closures marked as @mainactor
Original PR Description: ## 📜 Tickets
Jira ticket
Github issue

💡 Description

A closure is marked as @mainactor is already @sendable, in Swift 6 we don't need to mark the closure as @sendable if it is already marked as @mainactor

🎥 Demos

Before	After

Demo

📝 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

Original PR URL: mozilla-mobile#31547