Fix use of MessagePackValue.integerValue for .uint(Int64.max)

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Author: a2

Sources/MessagePack/ConvenienceProperties.swift

@@ -48,7 +48,7 @@ extension MessagePackValue {
         switch self {
         case .int(let value):
             return value
-        case .uint(let value) where value < UInt64(Int64.max):
+        case .uint(let value) where value <= UInt64(Int64.max):
             return Int64(value)
         default:
             return nil