chore: add .net9 target, remove .net6 target, upgrade sourcelink

Author: ascott18

src/IntelliTect.AspNetCore.SignalR.SqlServer/IntelliTect.AspNetCore.SignalR.SqlServer.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
 	<PropertyGroup>
-		<TargetFrameworks>net6.0;net8.0</TargetFrameworks>
+		<TargetFrameworks>net8.0;net9.0</TargetFrameworks>
 		<GenerateDocumentationFile>true</GenerateDocumentationFile>
 
 		<!-- Sourcelink: -->
@@ -12,7 +12,7 @@
 	</PropertyGroup>
 
 	<ItemGroup>
-		<PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
+		<PackageReference Include="Microsoft.SourceLink.GitHub" Version="8.0.0" PrivateAssets="All" />
 
 		<PackageReference Include="MessagePack" Version="2.5.187" />
 		<PackageReference Include="Microsoft.Data.SqlClient" Version="5.2.2" />