Update Xcode version to 16.4 in workflow (#3452)

Author: buenaflor

.github/workflows/testflight.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
       - uses: actions/checkout@v6
       - uses: subosito/flutter-action@fd55f4c5af5b953cc57a2be44cb082c8f6635e8e # pin@v2.21.0
-      - run: xcodes select 16.3
+      - run: xcodes select 16.4
       - uses: ruby/setup-ruby@4c24fa5ec04b2e79eb40571b1cee2a0d2b705771 # pin@v1.278.0
         with:
           ruby-version: '2.7.5'