Use .NET 8 SDK to build project (#655)

+semver:patch

Author: hazzik

global.json

@@ -1,6 +1,6 @@
 {
     "sdk": {
-        "version": "6.0.403",
+        "version": "8.0.100",
         "rollForward": "latestFeature"
     }
 }

src/FluentNHibernate.sln

@@ -6,6 +6,8 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Common", "Common", "{83F176
 	ProjectSection(SolutionItems) = preProject
 		Directory.Build.props = Directory.Build.props
 		FluentKey.snk = FluentKey.snk
+		..\global.json = ..\global.json
+		..\appveyor.yml = ..\appveyor.yml
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Examples", "Examples", "{3D285AE0-E5CF-4923-B543-0D70E5C6DE18}"

src/FluentNHibernate/FluentNHibernate.csproj

@@ -9,6 +9,10 @@
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>../FluentKey.snk</AssemblyOriginatorKeyFile>
   </PropertyGroup>
+  
+  <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp2.0'">
+    <RuntimeFrameworkVersion>2.0.9</RuntimeFrameworkVersion>
+  </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="NHibernate" Version="5.3.3" />