Update target frameworks and xUnit runner version

Author: niemyjski

build/common.props

@@ -1,7 +1,7 @@
 <Project ToolsVersion="15.0">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.1;net8.0</TargetFrameworks>
+    <TargetFrameworks>net8.0</TargetFrameworks>
     <Product>Foundatio</Product>
     <Description>Pluggable foundation blocks for building distributed apps.</Description>
     <PackageProjectUrl>https://github.com/FoundatioFx/Foundatio.RabbitMQ</PackageProjectUrl>

tests/Directory.Build.props

@@ -8,7 +8,7 @@
   <ItemGroup>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.14.1" />
     <PackageReference Include="xunit" Version="2.9.3" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.4" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.1.5" />
 
     <PackageReference Include="GitHubActionsTestLogger" Version="2.4.1" PrivateAssets="All" />