Fix test warning (#5558)

* Introduce JsonProvider.

It will ensure that classes are using the correct Json instances in the unit tests.

* Avoid creating a Json instance many times.

* Update ref.

app/src/main/kotlin/io/element/android/x/di/AppModule.kt

@@ -35,7 +35,6 @@ import kotlinx.coroutines.CoroutineName
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.MainScope
 import kotlinx.coroutines.plus
-import kotlinx.serialization.json.Json
 import java.io.File
 
 @BindingContainer
@@ -121,10 +120,4 @@ object AppModule {
     fun providesEmojibaseProvider(@ApplicationContext context: Context): EmojibaseProvider {
         return DefaultEmojibaseProvider(context)
     }
-
-    @Provides
-    @SingleIn(AppScope::class)
-    fun providesJson(): Json = Json {
-        ignoreUnknownKeys = true
-    }
 }