Upgraded unit test to use .net 5 instead of .net core 3.1

Emgu.CV.Test/Emgu.CV.Test.Netcore/Emgu.CV.Test.Netcore.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>
@@ -27,7 +27,7 @@
 
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="13.0.1" />
-    <PackageReference Include="nunit" Version="3.13.1" />
+    <PackageReference Include="nunit" Version="3.13.2" />
     <PackageReference Include="NUnit3TestAdapter" Version="3.17.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>