Fix typo in variable name: hasExplictValue -> hasExplicitValue

[voroninp]

Fix typo in variable name

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Summary of the changes (Less than 80 chars)

Description

I was looking at the source code and noticed there's a typo: hasExplictValue but should be hasExplicitValue.

[voroninp]

@mkArtakMSFT , hm... I'm surprised to see failed tests =)

[amcasey]

Failure is in Microsoft.AspNetCore.SignalR.StackExchangeRedis.Tests.RedisEndToEndTests.CanSendAndReceiveUserMessagesFromMultipleConnectionsWithSameUser(transportType: LongPolling, protocolName: "messagepack"), which is tracked by #55954