chore: update analyzers project to dotnet6 (#184)

Author: Meir017

src/FluentAssertions.Analyzers/FluentAssertions.Analyzers.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
     <LangVersion>latest</LangVersion>
     <RootNamespace>FluentAssertions.Analyzers</RootNamespace>