Use Xcode 26.3 CI image

[twstokes]

Description

Uses the Xcode 26.3 CI image.

Testing instructions

[dangermattic]

	1 Message
📖	This PR is still a Draft: some checks will be skipped.

Generated by 🚫 Danger

[wpmobilebot]

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

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	31599
	Version	PR #25396
	Bundle ID	com.jetpack.alpha
	Commit	af9e206
	Installation URL	38mfl0qv1qv48

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

[wpmobilebot]

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

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	31599
	Version	PR #25396
	Bundle ID	org.wordpress.alpha
	Commit	af9e206
	Installation URL	3816hkq6c97s8

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

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[twstokes]

I used this one to test the new image, but feel free to close or merge as you see fit.