Bump Verify.Xunit from 26.3.1 to 26.4.0 (#1825)

Bumps [Verify.Xunit](https://github.com/VerifyTests/Verify) from 26.3.1 to 26.4.0.
- [Release notes](https://github.com/VerifyTests/Verify/releases)
- [Commits](VerifyTests/Verify@26.3.1...26.4.0)

---
updated-dependencies:
- dependency-name: Verify.Xunit
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

test/Microsoft.OpenApi.Tests/Microsoft.OpenApi.Tests.csproj

@@ -15,7 +15,7 @@
     <PackageReference Include="Moq" Version="4.20.71" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="SharpYaml" Version="2.1.1" />
-    <PackageReference Include="Verify.Xunit" Version="26.3.1" />
+    <PackageReference Include="Verify.Xunit" Version="26.4.0" />
     <PackageReference Include="xunit" Version="2.9.0" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.8.2" PrivateAssets="all" />
     <PackageReference Include="Microsoft.CSharp" Version="4.7.0" />