Skip fetching context of private posts

[AndrewKvalheim]

From my timeline FediFetcher is repeatedly attempting to access private posts:

2024-07-01 17:16:27.362 PDT: Error getting context for toot https://example.com/@example/xxxxxxxxxxxxxxxx. Status code: 404
2024-07-01 17:16:37.445 PDT: Error getting context for toot https://example.com/@example/xxxxxxxxxxxxxxxx. Status code: 404
2024-07-01 17:16:44.915 PDT: Error getting context for toot https://example.com/@example/xxxxxxxxxxxxxxxx. Status code: 404
2024-07-01 17:16:51.760 PDT: Error getting context for toot https://example.com/@example/xxxxxxxxxxxxxxxx. Status code: 404

This will never succeed, so better to skip those requests.

[nanos]

Nice one! Thank you!