Xcode 16: prepare to have betas using Xcode 16 beta

[leandroalonso]

• Changes the CI image to Xcode 16 beta
• Add a question on finalize_release to ensure the image is set back to Xcode 15

To test

1. Run bundle exec fastlane finalize_release
2. When asked about the image type n
3. ✅ fastlane should fail with "Before submitting the app to release please change the CI image to xcode-15.4"

Also, CI must be 🟢.

Checklist

• I have considered if this change warrants user-facing release notes and have added them to CHANGELOG.md if necessary.
• I have considered adding unit tests for my changes.
• I have updated (or requested that someone edit) the spreadsheet to reflect any new or changed analytics.

[dangermattic]

🚫	Style/NegatedIf: Favor unless over if for negative conditions.

[leandroalonso]

@danielebogo is that bot friend of yours? 🤣

[dangermattic]

	1 Warning
⚠️	This PR is assigned to the milestone 7.71 ❄️. 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

[bjtitus]

Would it make sense to automate this check so it's only really shown when we know the IMAGE_ID is wrong?

Suggested change

	# Temporarily: we should remove after moving to Xcode 16 in definitive
	sh("grep 'IMAGE_ID: xcode-15.4' #{PROJECT_ROOT_FOLDER}/.buildkite/release-builds.yml", error_callback: ->(result) {
	# Temporarily: we should remove after moving to Xcode 16 in definitive
	unless UI.confirm('Please ensure Xcode image is set to xcode-15.4 before moving forward, if it is, type y. If not, type n.')
	UI.user_error!('Before submitting the app to release please change the CI image to xcode-15.4')
	end
	})

[leandroalonso]

Hmm, I think that might be good

Although I pretend to remove all of that asap 😆

[bjtitus]

Looked good in testing. Left one small comment about whether we should automate the check for IMAGE_ID so it isn't as easy to overlook. Not sure if that's worth the extra effort but thought I'd suggest it.