[Tooling] Update CI image from `xcode-16.1` to `xcode-16.1-v4`

[spencertransier]

What it does

This updates the CI image from xcode-16.1 to xcode-16.1.v4. The original 16.1 image only had 92GB of space. The v4 image was upgraded to use 120GB instead.

It also updates the CI Toolkit from 3.3.0 to 3.7.1 and extracts that into a separate var to match our pattern in other repos.

How to test

Good to go as long as CI is green.

[dangermattic]

	1 Warning
:warning:	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 :no_entry_sign: Danger

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📲 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	pr23822-90c1aa6
	Version	25.4.2
	Bundle ID	com.jetpack.alpha
	Commit	90c1aa6fc9d2ff89596e42a11e708c8d83153f22
	App Center Build	jetpack-installable-builds #10124

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[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	pr23822-90c1aa6
	Version	25.4.2
	Bundle ID	org.wordpress.alpha
	Commit	90c1aa6fc9d2ff89596e42a11e708c8d83153f22
	App Center Build	WPiOS - One-Offs #11083

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