[netcore] Make System.Data.Tests.SqlTypes.SqlDoubleTest.ReadWriteXmlTest Pass

[steveisok]

Fails similarly to #15174, but w/ a different type.

System.Data.Tests.SqlTypes.SqlDoubleTest.ReadWriteXmlTest [FAIL]
      System.InvalidOperationException : There is an error in XML document (0, 0).
      ---- System.InvalidProgramException : Invalid IL code in Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationReaderSqlDouble:Read1_double (): IL_00bc: castclass 0x0100000d
      
      
      Stack Trace:
           at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle, XmlDeserializationEvents events)
           at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader, String encodingStyle)
           at System.Xml.Serialization.XmlSerializer.Deserialize(XmlReader xmlReader)
           at System.Data.Tests.SqlTypes.SqlDoubleTest.ReadWriteXmlTestInternal(String xml, Double testval, String unit_test_id)
           at System.Data.Tests.SqlTypes.SqlDoubleTest.ReadWriteXmlTest()
           at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
        ----- Inner Stack Trace -----
           at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

Determine why and make the test pass.

[MaximLipnin]

This issue was addressed in dotnet/runtime#2087 and I had no repro for this test within the work dotnet/runtime#2087. I'm closing it.