Use Ruby 3.4.9, Bundler 4.0.22, and Xcode 26.6

[iangmaia]

Fixes AINFRA-2860

• Update Ruby to 3.4.9 and Bundler to 4.0.22
• Use the Xcode 26.6 CI image (the first one with Ruby 3.4.9)
• Run tests on iPhone 17
• Raise the Xcode project's deployment target to iOS 15, matching Package.swift

To test (Xcode 26.6):

bundle install
bundle exec fastlane test
bundle exec rubocop

Note: on Xcode 27, the Example app will need the UIScene life cycle to launch on iOS 27 simulators.

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PR submission checklist:

• I have considered adding unit tests where possible. (No behavior change.)
• I have considered adding accessibility improvements for my changes. (N/A)
• I have considered if this change warrants release notes and have added them to the appropriate section in the CHANGELOG.md if necessary. (Tooling only, so none needed.)

🤖 Generated with Claude Code

[Copilot]

Copilot review overview

🟢 Approval recommended

The tooling and deployment-target updates are consistent with the stated purpose and existing package requirements.

Review effort: Balanced
Findings: None

What changed in this PR

Updates the development and CI toolchain while aligning deployment targets.

Changes:

• Upgrades Ruby, Bundler, and the Buildkite Xcode image.
• Runs tests on iPhone 17.
• Aligns the Xcode project with the iOS 15 package minimum.

File	Description
.ruby-version	Selects Ruby 3.4.9.
.buildkite/​pipeline.yml	Uses Xcode 26.6.
Gemfile.lock	Records Bundler 4.0.22.
fastlane/​Fastfile	Tests with iPhone 17.
MediaEditor.xcodeproj/​project.pbxproj	Raises deployment targets to iOS 15.

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[AliSoftware]

I'm pretty sure this won't cause any problem because I doubt any adopter of this library is using a deployment target <15.0 nowadays (I think WPiOS is the only one of our own apps using it?); but worth noting that this will thus be a breaking change to the library for the next time we'll do a new version…