Bump Verify.Xunit from 20.8.2 to 21.0.0 in /src (#455)

Bumps [Verify.Xunit](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.Xunit
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

src/Tests/Tests.csproj

@@ -7,7 +7,7 @@
     <PackageReference Include="Xunit" Version="2.5.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.5.0" PrivateAssets="all" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.7.2" />
-    <PackageReference Include="Verify.Xunit" Version="20.8.2" />
+    <PackageReference Include="Verify.Xunit" Version="21.0.0" />
     <PackageReference Include="MarkdownSnippets.MsBuild" Version="25.1.0" />
     <ProjectReference Include="..\NodaTime.Bogus\NodaTime.Bogus.csproj" />
     <PackageReference Include="ProjectDefaults" Version="1.0.91" PrivateAssets="all" />