Bug : Sending a message

- Issue
Sending a message and navigating to the chat list crashes and closes the app

https://github.com/android/socialite/assets/38935359/ee95ae46-76b0-4249-ad4f-fc3986f6301e

- StackTrace
```
com...gle.android.samples.socialite E FATAL EXCEPTION: pool-2-thread-1
Process: com.google.android.samples.socialite, PID: 2421
java.lang.IllegalArgumentException: Context is required to resolve the file uri of the icon: content://com.google.android.samples.socialite/icon/1
at androidx.core.graphics.drawable.IconCompat$Api23Impl.toIcon(IconCompat.java:1297)
at androidx.core.graphics.drawable.IconCompat.toIcon(IconCompat.java:529)
at androidx.core.graphics.drawable.IconCompat.toIcon(IconCompat.java:517)
at androidx.core.app.Person$Api28Impl.toAndroidPerson(Person.java:427)
at androidx.core.app.Person.toAndroidPerson(Person.java:152)
at androidx.core.app.NotificationCompatBuilder.(NotificationCompatBuilder.java:263)
at androidx.core.app.NotificationCompat$Builder.build(NotificationCompat.java:2531)
at com.google.android.samples.socialite.repository.NotificationHelper.showNotification(NotificationHelper.kt:274)
at com.google.android.samples.socialite.repository.NotificationHelper.showNotification$default(NotificationHelper.kt:159)
at com.google.android.samples.socialite.repository.ChatRepository$sendMessage$2.invokeSuspend(ChatRepository.kt:92)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:108)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
at java.lang.Thread.run(Thread.java:919)
Suppressed: kotlinx.coroutines.internal.DiagnosticCoroutineContextException: [StandaloneCoroutine{Cancelling}@285c18d, java.util.concurrent.Executors$FinalizableDelegatedExecutorService@3fa8f42]
```

Start at NotificationHelper.kt:274 and ChatRepository.kt:92, following the stack trace through notification construction and the icon URI conversion. Reproduce sending a message and navigating to the chat list, then verify that this flow no longer crashes or closes the app.

Written by the indexing model from the issue text.