Revert "Upgrade to .NET 10"

This reverts commit 76338aa.

Author: jasontaylordev

samples/open-telemetry/prometheus-grafana/Core_10/Endpoint/Endpoint.csproj

@@ -2,13 +2,12 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net10.0</TargetFramework>
-    <LangVersion>preview</LangVersion>
-    <ImplicitUsings>enable</ImplicitUsings>
+    <TargetFrameworks>net9.0;net8.0</TargetFrameworks>
+    <LangVersion>12.0</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="NServiceBus" Version="10.0.0-alpha.1" />
+    <PackageReference Include="NServiceBus" Version="9.*" />
     <PackageReference Include="OpenTelemetry.Exporter.Prometheus.HttpListener" Version="1.*-*" />
   </ItemGroup>