[Fuzzing] Utf8JsonWriterFuzzer: Memory stream is not expandable.

[MihaZupan]

System.NotSupportedException: Memory stream is not expandable.
   at System.IO.MemoryStream.set_Capacity(Int32 value)
   at System.IO.MemoryStream.EnsureCapacity(Int32 value)
   at System.IO.MemoryStream.Write(ReadOnlySpan`1 buffer)
   at System.Text.Json.Utf8JsonWriter.Flush()
   at System.Text.Json.Utf8JsonWriter.Dispose()
   at DotnetFuzzing.Fuzzers.Utf8JsonWriterFuzzer.FuzzTarget(ReadOnlySpan`1 bytes) in Utf8JsonWriterFuzzer.cs:line 145

From #111332, cc: @PranavSenthilnathan

Example input (hex): 00000000000000002000 -- so just the fuzzer options, empty input

[dotnet-policy-service]

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