Retarget GmodNET.API to net6.0 tfm (#140)

Author: GlebChili

gm_dotnet_managed/GmodNET.API/GmodNET.API.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <Product>GmodNET API</Product>
     <Description>GmodNET API library contains all necessary interfaces to write a GmodNET module.</Description>