Bump NUnit3TestAdapter from 5.2.0 to 6.0.0 (#30)

Author: dependabot[bot]

MonthDiff.Tests/MonthDiff.Tests.csproj

@@ -11,7 +11,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.0.1" />
         <PackageReference Include="NUnit" Version="4.4.0" />
-        <PackageReference Include="NUnit3TestAdapter" Version="5.2.0" />
+        <PackageReference Include="NUnit3TestAdapter" Version="6.0.0" />
     </ItemGroup>
 
     <ItemGroup>