Change screenshot test to use RNG

Test: atest -c SettingsScreenshotRNGTests
 -- --test-arg
 com.android.tradefed.testtype.IsolatedHostTest:java-flags:
 -Drobolectric.graphicsMode=NATIVE
Fixes: 314807258
Change-Id: I4fa533c19d0b1386a7a4649ed88e3814816c1899

tests/screenshot/config/robolectric.properties

@@ -0,0 +1,16 @@
+# Copyright (C) 2023 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+sdk=NEWEST_SDK
+graphicsMode=NATIVE