Examples: Android+OpenGL3: update Gradle project, amend. (#8888, #8878)

examples/example_android_opengl3/android/gradle/libs.versions.toml

@@ -0,0 +1,8 @@
+[versions]
+agp = "8.12.0"
+kotlin = "2.0.21"
+
+[plugins]
+android-application = { id = "com.android.application", version.ref = "agp" }
+kotlin-android = { id = "org.jetbrains.kotlin.android", version.ref = "kotlin" }
+