Upgrade Xcode versions

Author: ann0see

.github/workflows/autobuild.yml

@@ -231,7 +231,7 @@ jobs:
             # Disable CodeQL on mac as it interferes with signing the binaries (signing hangs, see #2563 and #2564)
             run_codeql:             false
             # Latest Xcode which runs on macos-15:
-            xcode_version:          16.2.0
+            xcode_version:          16.4.0
             is_main_build_target:   true
 
           # Reminder: If Legacy is removed, be sure to add a dedicated job for CodeQL again.
@@ -250,12 +250,12 @@ jobs:
           - config_name:            iOS (artifacts)
             target_os:              ios
             building_on_os:         macos-15
-            base_command:           QT_VERSION=6.9.1 ./.github/autobuild/ios.sh
+            base_command:           QT_VERSION=6.7.3 ./.github/autobuild/ios.sh
             # Build failed with CodeQL enabled when last tested 03/2022 (#2490).
             # There are no hints that iOS is supposed to be supported by CodeQL.
             # Therefore, disable it:
             run_codeql:             false
-            xcode_version:          16.3.0
+            xcode_version:          16.4.0
 
           - config_name:            Windows (artifact+codeQL)
             target_os:              windows