Targeted tests to .net6 and changed runner to ubuntu-20.04

Author: jannejjj

.github/workflows/BuildAndTestOnEveryPush.yml

@@ -9,7 +9,7 @@ jobs:
 
   UbuntuBuild:
     name: Build on ubuntu-latest
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
 
     steps:
     - uses: actions/checkout@v1

Frends.Community.SQL.Tests/Frends.Community.SQL.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net471</TargetFramework>
+    <TargetFramework>net6.0</TargetFramework>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>