Bump Verify.NUnit from 20.8.2 to 21.0.0

Bumps [Verify.NUnit](https://github.com/VerifyTests/Verify) from 20.8.2 to 21.0.0.
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@20.8.2...21.0.0)

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

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

test/Html2Markdown.Test/Html2Markdown.Test.csproj

@@ -8,7 +8,7 @@
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
     <PackageReference Include="NUnit" Version="3.13.3" />
     <PackageReference Include="NUnit3TestAdapter" Version="4.5.0" />
-    <PackageReference Include="Verify.NUnit" Version="20.8.2" />
+    <PackageReference Include="Verify.NUnit" Version="21.0.0" />
   </ItemGroup>
 
   <ItemGroup>