ues LangVersion 13

Author: neuecc

src/MessagePack/MessagePack.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;netstandard2.1;net8.0;net9.0;net472</TargetFrameworks>
+    <LangVersion>13</LangVersion>
     <NoWarn>$(NoWarn);CS0649</NoWarn>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
     <DefineConstants Condition=" '$(TargetFramework)' == 'net8.0' or '$(TargetFramework)' == 'net9.0' or '$(TargetFramework)' == 'netstandard2.1' ">$(DefineConstants);SPAN_BUILTIN</DefineConstants>