build: Bump NUnit from 3.13.3 to 4.6.1

---
updated-dependencies:
- dependency-name: NUnit
  dependency-version: 4.6.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

APIMatic.Core.Test/APIMatic.Core.Test.csproj

@@ -16,7 +16,7 @@
             <PrivateAssets>all</PrivateAssets>
             <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
         </PackageReference>
-        <PackageReference Include="NUnit" Version="3.13.3" />
+        <PackageReference Include="NUnit" Version="4.6.1" />
         <PackageReference Include="NUnit3TestAdapter" Version="6.1.0" />
         <PackageReference Include="RichardSzalay.MockHttp" Version="7.0.0" />
         <PackageReference Include="System.Net.Http.Json" Version="10.0.2" />