Bump NUnit from 3.14.0 to 4.0.0 (#757)

Bumps [NUnit](https://github.com/nunit/nunit) from 3.14.0 to 4.0.0.
- [Release notes](https://github.com/nunit/nunit/releases)
- [Changelog](https://github.com/nunit/nunit/blob/master/CHANGES.md)
- [Commits](nunit/nunit@v3.14.0...v4.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

src/ApprovalTests.Tests/ApprovalTests.Tests.csproj

@@ -9,7 +9,7 @@
     <PackageReference Include="itext7.bouncy-castle-adapter" Version="8.0.2" />
     <PackageReference Include="MarkdownSnippets.MsBuild" Version="25.1.0" />
     <PackageReference Include="itext7" Version="8.0.2" />
-    <PackageReference Include="NUnit" Version="3.14.0" />
+    <PackageReference Include="NUnit" Version="4.0.0" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.8.0" />
     <PackageReference Include="System.Management" Version="6.0.2" />