Support .NET 9

Author: Odonno

src/Dahomey.Cbor.Tests/Dahomey.Cbor.Tests.csproj

@@ -1,9 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net6.0;net7.0;net8.0</TargetFrameworks>
+    <TargetFrameworks>net6.0;net7.0;net8.0;net9.0</TargetFrameworks>
     <IsPackable>false</IsPackable>
-    <LangVersion>12.0</LangVersion>
+    <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/Dahomey.Cbor/Dahomey.Cbor.csproj

@@ -1,8 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;net6.0;net7.0;net8.0</TargetFrameworks>
-    <LangVersion>12.0</LangVersion>
+    <TargetFrameworks>netstandard2.0;net6.0;net7.0;net8.0;net9.0</TargetFrameworks>
+    <LangVersion>latest</LangVersion>
     <Nullable>enable</Nullable>
     <PackageReleaseNotes>cf. https://github.com/dahomey-technologies/Dahomey.Cbor/releases/tag/$(Version)</PackageReleaseNotes>
     <Authors>Michaël Catanzariti</Authors>