[WebRequest] DefaultMaximumErrorResponseLength should be KB

[ManickaP]

#97537 follow up. DefaultMaximumErrorResponseLength should be interpreted as kilobytes, not bytes, to behave the same as in Framework, see https://referencesource.microsoft.com/#System/net/System/Net/HttpWebRequest.cs,6150

Discovered in https://github.com/dotnet/dotnet-api-docs/pull/10138/files#r1688603374

cc @liveans

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