Update xcodeproj requirement from < 1.26.0 to < 1.29.0 in /example

Updates the requirements on [xcodeproj](https://github.com/cocoapods/xcodeproj) to permit the latest version.
- [Release notes](https://github.com/cocoapods/xcodeproj/releases)
- [Changelog](https://github.com/CocoaPods/Xcodeproj/blob/master/CHANGELOG.md)
- [Commits](https://github.com/cocoapods/xcodeproj/compare/0.0.1...1.28.1)

---
updated-dependencies:
- dependency-name: xcodeproj
  dependency-version: 1.28.1
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

example/Gemfile

@@ -6,7 +6,7 @@ ruby ">= 2.6.10"
 # Exclude problematic versions of cocoapods and activesupport that causes build failures.
 gem 'cocoapods', '>= 1.13', '!= 1.15.0', '!= 1.15.1'
 gem 'activesupport', '>= 6.1.7.5', '!= 7.1.0'
-gem 'xcodeproj', '< 1.26.0'
+gem 'xcodeproj', '< 1.29.0'
 gem 'concurrent-ruby', '< 1.3.4'
 
 # Ruby 3.4.0 has removed some libraries from the standard library.