[csharp][booking][01_base] Upgrade to .Net 5.0

Author: solvingproblemswithtechnology

examples/csharp/csharp-booking-01_base/csharp-booking-01_base.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <TargetFramework>net5.0</TargetFramework>
     <RootNamespace>tv.codely</RootNamespace>
   </PropertyGroup>