[BUG]: JSON parse error when event=pull_request and action=milestoned

[jamesyao-msft]

What happened?

Message: 
System.Text.Json.JsonException : The JSON value could not be converted to Octokit.Webhooks.Events.PullRequestEvent. Path: $ | LineNumber: 0 | BytePositionInLine: 30483.

Stack Trace: 
WebhookConverter1.Read(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options) JsonConverter1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
JsonConverter1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state) JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan1 utf8Json, JsonTypeInfo jsonTypeInfo, Nullable1 actualByteCount) JsonSerializer.ReadFromSpan[TValue](ReadOnlySpan1 json, JsonTypeInfo jsonTypeInfo)
JsonSerializer.Deserialize[TValue](String json, JsonSerializerOptions options)
WebhookEventProcessor.DeserializeWebhookEvent(WebhookHeaders headers, String body)

Versions

Octokit.Webhooks.net v1.3.5

Relevant log output

No response

Code of Conduct

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[jamesyao-msft]

Root cause might be "milestoned" action was not handled in JSON converter. Consider making it not throw exception.

[JamieMagee]

Thanks for the bug report. It looks like it was added to https://github.com/github/rest-api-description recently. I usually pull types from https://github.com/octokit/webhooks, but it hasn't been updated yet.

For not throwing, this should be resolved with #98