Update test_iphone_15 lane to use iPhone 16 Pro simulator

Updated the test_iphone_15 lane to use the most recent iPhone Pro simulator
(iPhone 16 Pro) which is available in Xcode 16+ for better compatibility
with the latest Xcode image 26+.

Author: claude

fastlane/Fastfile

@@ -62,12 +62,12 @@ platform :ios do
   ## TESTING & CODE COVERAGE ##
   #############################
 
-  desc 'Run tests using iPhone 15 sim'
+  desc 'Run tests using iPhone 16 Pro sim'
   lane :test_iphone_15 do
     run_tests_for_device(
       project_base_name: project_base_name,
       schemes: schemes_to_test,
-      device: 'iPhone 15'
+      device: 'iPhone 16 Pro'
     )
   end
 

fastlane/README.md

@@ -65,7 +65,7 @@ cache_prefix - optional.  Default is project_base_name.
 [bundle exec] fastlane ios test_iphone_15
 ```
 
-Run tests using iPhone 15 sim
+Run tests using iPhone 16 Pro sim
 
 ### ios test_iphone_pro