Avoid crash if multiple instances of ClearDatabaseScreen opened

Fixes #8851

I guess we might want to do this for all screens? Maybe?

app/src/main/java/eu/kanade/presentation/more/settings/screen/ClearDatabaseScreen.kt

@@ -31,6 +31,7 @@ import cafe.adriel.voyager.core.model.StateScreenModel
 import cafe.adriel.voyager.core.model.coroutineScope
 import cafe.adriel.voyager.core.model.rememberScreenModel
 import cafe.adriel.voyager.core.screen.Screen
+import cafe.adriel.voyager.core.screen.uniqueScreenKey
 import cafe.adriel.voyager.navigator.LocalNavigator
 import cafe.adriel.voyager.navigator.currentOrThrow
 import eu.kanade.domain.source.interactor.GetSourcesWithNonLibraryManga
@@ -58,6 +59,8 @@ import uy.kohesive.injekt.api.get
 
 class ClearDatabaseScreen : Screen {
 
+    override val key = uniqueScreenKey
+
     @Composable
     override fun Content() {
         val context = LocalContext.current