Bugfix FXIOS-11034 Avoid non-MT access in closeTab()

[mattreaganmozilla]

📜 Tickets

Partial fix for broader issue mentioned in 11034
#24085

💡 Description

Avoid non-MT access to tabs collection within closeTab. Although the principal function it calls (removeTab) is already @MainActor the getters called beforehand are still problematic, as they can end up reading the tabs array in a background thread while work on the MT may be writing to it.

📝 Checklist

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• Filled in the above information (tickets numbers and description of your work)
• Updated the PR name to follow our PR naming guidelines
• Wrote unit tests and/or ensured the tests suite is passing
• When working on UI, I checked and implemented accessibility (minimum Dynamic Text and VoiceOver)
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[mattreaganmozilla]

@dataports @OrlaM LMK if any concerns. It's hard to see how this would cause any complications but I know there's a lot of work happening currently in our tab middlewares.

[mattreaganmozilla]

Also related (another thread issue with tabs): #24028

[mobiletest-ci-bot]

	Messages
📖	Project coverage: 34.17%
📖	Edited 1 files
📖	Created 0 files

Client.app: Coverage: 32.39

File	Coverage
TabManagerMiddleware.swift	7.13%	⚠️

Generated by 🚫 Danger Swift against 41ce218

[dataports]

Makes sense to me 👍