Align `targetSdk` to 34 in `AndroidTestConventionPlugin.kt`

Initial update was applied in https://github.com/android/nowinandroid/pull/814

build-logic/convention/src/main/kotlin/AndroidTestConventionPlugin.kt

@@ -31,7 +31,7 @@ class AndroidTestConventionPlugin : Plugin<Project> {
 
             extensions.configure<TestExtension> {
                 configureKotlinAndroid(this)
-                defaultConfig.targetSdk = 31
+                defaultConfig.targetSdk = 34
                 configureGradleManagedDevices(this)
             }
         }