Use Android 14 for instrumented tests again (#1535)

app/build.gradle.kts

@@ -106,7 +106,9 @@ android {
             localDevices {
                 create("virtual") {
                     device = "Pixel 3"
-                    apiLevel = 35
+                    // TBD: API level 35 and higher causes network tests to fail sometimes, see https://github.com/bitfireAT/davx5-ose/issues/1525
+                    // Suspected reason: https://developer.android.com/about/versions/15/behavior-changes-all#background-network-access
+                    apiLevel = 34
                     systemImageSource = "aosp-atd"
                 }
             }