target .Net 6 instead of both 5 and 6

Getting consistent build error in VS2022 where the compiled plugin dll is locked down by a process.

Author: jjw24

Flow.Launcher.Plugin/Flow.Launcher.Plugin.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>net6.0-windows;net5.0-windows</TargetFrameworks>
+    <TargetFramework>net6.0-windows</TargetFramework>
     <ProjectGuid>{8451ECDD-2EA4-4966-BB0A-7BBC40138E80}</ProjectGuid>
     <UseWPF>true</UseWPF>
     <OutputType>Library</OutputType>