Make Xcode report concurrency warnings on the Modules package

[crazytonyli]

This PR will introduce about 100+ more warnings. I'll "address" (probably just @unchecked Sendable) them in follow up PRs.

As the warnings gone, I'll remove the compiler flags, which means compiler will report errors if new code violates concurrency rules.

Regression Notes

1. Potential unintended areas of impact

2. What I did to test those areas of impact (or what existing automated tests I relied on)

3. What automated tests I added (or what prevented me from doing so)

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

Testing checklist:

• WordPress.com sites and self-hosted Jetpack sites.
• Portrait and landscape orientations.
• Light and dark modes.
• Fonts: Larger, smaller and bold text.
• High contrast.
• VoiceOver.
• Languages with large words or with letters/accents not frequently used in English.
• Right-to-left languages. (Even if translation isn’t complete, formatting should still respect the right-to-left layout)
• iPhone and iPad.
• Multi-tasking: Split view and Slide over. (iPad)

[dangermattic]

	2 Warnings
⚠️	Modules/Package.swift was changed without updating its corresponding Package.resolved. Please resolve the Swift packages as appropriate to your project setup (e.g. in Xcode or by running swift package resolve).
⚠️	This PR is assigned to the milestone 25.6. The due date for this milestone has already passed. Please assign it to a milestone with a later deadline or check whether the release for this milestone has already been finished.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress Alpha by scanning the QR code below to install the corresponding build.

	App Name	WordPress Alpha
	Configuration	Release-Alpha
	Build Number	pr23838-c79e812
	Version	25.5
	Bundle ID	org.wordpress.alpha
	Commit	c79e812
	App Center Build	WPiOS - One-Offs #11159

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack Alpha by scanning the QR code below to install the corresponding build.

	App Name	Jetpack Alpha
	Configuration	Release-Alpha
	Build Number	pr23838-c79e812
	Version	25.5
	Bundle ID	com.jetpack.alpha
	Commit	c79e812
	App Center Build	jetpack-installable-builds #10197

Automatticians: You can use our internal self-serve MC tool to give yourself access to App Center if needed.

[kean]

Apple recommends to work in waves: enable the flags, fix some issues, disable the flags. Continue until there are no more warnings/errors and the flags can be enabled permanently.

[crazytonyli]

@kean I thought enabling the concurrency checks (with errors) earlier would be nice, especially considering we have added @unchecked Sendable everywhere (in #23527) to ignore the concurrency check warnings.

[kean]

I'm only suggesting to do it the other way around: fix warnings, then enable the flags in trunk.

[crazytonyli]

@kean I have removed .enableUpcomingFeature("StrictConcurrency"). This PR now should have no impact on the existing code. But future new targets in Modules should be on Swift v6 and get strict concurrency checks.

[kean]

The previous version seemed a bit more readable.

[crazytonyli]

Swift compiler reports a concurrency check error on the previous version. I can't remember the exact error message, but it's related to the variable being a global variable.