Update target frameworks to .NET 8.0 (#905)

The project file `Appium.Net.Integration.Tests.csproj` has been modified to update the target frameworks. The project was previously targeting .NET Framework 4.8 and .NET 6.0. The change replaces .NET 6.0 with .NET 8.0, so the project now targets .NET Framework 4.8 and .NET 8.0. This update likely reflects a move to support the latest version of .NET.

Author: Dor-bl

test/integration/Appium.Net.Integration.Tests.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>net48;net6.0</TargetFrameworks>
+    <TargetFrameworks>net48;net8.0</TargetFrameworks>
 	<LangVersion>latest</LangVersion>
   </PropertyGroup>
   <ItemGroup>