Bump Validation and Xunit.SkippableFact (#384)

Bumps [Validation](https://github.com/AArnott/Validation) and [Xunit.SkippableFact](https://github.com/AArnott/Xunit.SkippableFact). These dependencies needed to be updated together.

Updates `Validation` from 2.6.68 to 2.5.51
- [Release notes](https://github.com/AArnott/Validation/releases)
- [Commits](AArnott/Validation@v2.6.68...v2.5.51)

Updates `Xunit.SkippableFact` from 1.4.13 to 1.5.23
- [Release notes](https://github.com/AArnott/Xunit.SkippableFact/releases)
- [Commits](AArnott/Xunit.SkippableFact@v1.4.13...v1.5.23)

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

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

Author: dependabot[bot]

tests/NRedisStack.Tests/NRedisStack.Tests.csproj

@@ -33,7 +33,7 @@
     <PackageReference Include="xunit.assert" Version="2.4.1" />
     <PackageReference Include="BouncyCastle.Cryptography" Version="2.5.0" />
     <PackageReference Include="Microsoft.Azure.StackExchangeRedis" Version="3.1.0" />
-    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.5.23" />
   </ItemGroup>
 
   <ItemGroup>