Fix security vulnerability in WixToolset.Sdk and update to .NET 8.0

Changes:
- Updated WixToolset.Sdk from 4.0.0 to 6.0.2 (fixes high severity vulnerability GHSA-rf39-3f98-xr7r)
- Updated FwInstaller output path from net6.0 to net8.0

This resolves the security warnings in the Error List and aligns the installer project with the .NET 8.0 upgrade.

Author: TechieGuy12

FwInstaller/FwInstaller.wixproj

@@ -1,6 +1,6 @@
-<Project Sdk="WixToolset.Sdk/4.0.0">
+<Project Sdk="WixToolset.Sdk/6.0.2">
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
-    <OutputPath>..\src\bin\Release\net6.0\publish\win-x64</OutputPath>
+    <OutputPath>..\src\bin\Release\net8.0\publish\win-x64</OutputPath>
   </PropertyGroup>
   <ItemGroup>
     <None Include="config.xml.sample" />