Make app screenshots use the app theme

Change-Id: I30c3f9028671a8c48e6c49b9baeb186f5eb75479

app/src/testDemo/kotlin/com/google/samples/apps/nowinandroid/ui/NiaAppScreenSizesScreenshotTests.kt

@@ -37,6 +37,7 @@ import com.google.samples.apps.nowinandroid.core.data.repository.TopicsRepositor
 import com.google.samples.apps.nowinandroid.core.data.repository.UserDataRepository
 import com.google.samples.apps.nowinandroid.core.data.repository.UserNewsResourceRepository
 import com.google.samples.apps.nowinandroid.core.data.util.NetworkMonitor
+import com.google.samples.apps.nowinandroid.core.designsystem.theme.NiaTheme
 import com.google.samples.apps.nowinandroid.core.testing.util.DefaultRoborazziOptions
 import com.google.samples.apps.nowinandroid.uitesthiltmanifest.HiltComponentActivity
 import dagger.hilt.android.testing.BindValue
@@ -140,6 +141,7 @@ class NiaAppScreenSizesScreenshotTests {
             ) {
                 TestHarness(size = DpSize(width, height)) {
                     BoxWithConstraints {
+                        NiaTheme {
                             NiaApp(
                                 windowSizeClass = WindowSizeClass.calculateFromSize(
                                     DpSize(maxWidth, maxHeight),
@@ -151,6 +153,7 @@ class NiaAppScreenSizesScreenshotTests {
                     }
                 }
             }
+        }
 
         composeTestRule.onRoot()
             .captureRoboImage(