ci: build iOS with Xcode 26

@nativescript/core 9.0.20 uses the iOS 26 interactiveContentPopGestureRecognizer
API when running on iOS 26+. Apps built with the iOS 18 SDK (Xcode 16) lack the
API in their generated metadata, crashing the test app on the iOS 26.2 simulator.
Build with Xcode 26 so the metadata matches the simulator runtime.

Author: edusperoni

.github/workflows/build.yml

@@ -13,7 +13,7 @@ env:
   # NativeScript CLI (provides the `ns` binary the nx test executor spawns)
   NS_CLI_VERSION: latest
   # iOS (runner label is set on the job's `runs-on`, it can't read env)
-  XCODE_VERSION: "^16.0"
+  XCODE_VERSION: "^26.0"
   # Android
   JAVA_VERSION: "21"
   ANDROID_API: "34"