Bump NUnit from 4.3.2 to 4.4.0 (#42)

Author: dependabot[bot]

test/Diffs.Test.csproj

@@ -10,7 +10,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="NUnit" Version="4.3.2" />
+    <PackageReference Include="NUnit" Version="4.4.0" />
     <PackageReference Include="NUnit.Analyzers" Version="4.10.0">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>