flet_example/android: extractNativeLibs=true (match bridge_example)

serious_python_android ships libpythonbundle.so / libpythonsitepackages.so
which are ZIP archives masquerading as .so files (so they ride the
standard jniLibs packaging path). AGP 8.x defaults to NOT extracting
native libs out of the APK at install time, leaving them inaccessible
as on-disk files — which serious_python_android.dart's run() needs.

Setting `android:extractNativeLibs="true"` on the <application> tag
restores the pre-AGP-8 behavior; matches the same setting in
bridge_example/android/app/src/main/AndroidManifest.xml which has been
green on Android.

Author: FeodorFitsner

src/serious_python/example/flet_example/android/app/src/main/AndroidManifest.xml

@@ -2,7 +2,8 @@
     <application
         android:label="flet_example"
         android:name="${applicationName}"
-        android:icon="@mipmap/ic_launcher">
+        android:icon="@mipmap/ic_launcher"
+        android:extractNativeLibs="true">
         <activity
             android:name=".MainActivity"
             android:exported="true"