Fix projects definitions

AdventOfCode2018.Tests/AdventOfCode2018.Tests.csproj

@@ -2,6 +2,8 @@
 
   <PropertyGroup>
     <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <RootNamespace>AdventOfCode2018.Tests</RootNamespace>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>

AdventOfCode2018.Tests/Day04_Tests.cs

@@ -1,6 +1,4 @@
-using System.Collections.Generic;
-
-namespace AdventOfCode2018.Tests;
+namespace AdventOfCode2018.Tests;
 
 public class Day04_Tests
 {

AdventOfCode2018.Tests/Day10_Tests.cs

@@ -1,6 +1,4 @@
-using System;
-
-namespace AdventOfCode2018.Tests;
+namespace AdventOfCode2018.Tests;
 
 public class Day10_Tests
 {