deserialization issue affecting APIGatewayCustomAuthorizerContext

### Describe the bug

Not able to consume values returned by a Lambda Authorizer; they are not there even if they are present in the input JSON

### Expected Behavior

Dictionary properly set with keys and values

### Current Behavior

No values

### Reproduction Steps

Websocket API with an authorizer; try to access any authorizer context property (like principalId)
Use the new "Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer" (which is default)

### Possible Solution

As a workaround, the old "Amazon.Lambda.Serialization.Json.JsonSerializer" using the Newtonsoft library seems to work just fine.

### Additional Information/Context

using Amazon.Lambda.Serialization.SystemTextJson.DefaultLambdaJsonSerializer
"Authorizer": {
"principalId": {
"ValueKind": 3
},
"integrationLatency": {
"ValueKind": 4
},
"authn": {
"ValueKind": 3
}
}

using the legacy Amazon.Lambda.Serialization.Json.JsonSerializer
"Authorizer": {
"principalId": "***********************",
"integrationLatency": 9516,
"authn": "None"
},

### AWS .NET SDK and/or Package version used

Amazon.Lambda.Serialization.SystemTextJson v2.3.0

### Targeted .NET Platform

.net core 3.1

### Operating System and version

any