Fixed the support for test projects.

Author: SpartaDeveloper93

src/GeoJSON.Text.Test.Unit/GeoJSON.Text.Test.Unit.csproj

@@ -4,7 +4,7 @@
     <ProjectGuid>{6C93B314-9208-4684-B873-172F7EC81689}</ProjectGuid>
     <RootNamespace>GeoJSON.Text.Tests</RootNamespace>
     <AssemblyName>GeoJSON.Text.Tests</AssemblyName>
-    <TargetFrameworks>net462,net6.0;net7.0;netcoreapp3.1</TargetFrameworks>
+    <TargetFrameworks>net6.0;net7.0;netstandard2.0</TargetFrameworks>
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
     <LangVersion>10</LangVersion>
   </PropertyGroup>