Bump Microsoft.NETFramework.ReferenceAssemblies and Xunit.SkippableFact

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

Updates `Microsoft.NETFramework.ReferenceAssemblies` from 1.0.3 to 1.0.3
- [Commits](https://github.com/Microsoft/dotnet/commits)

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: Microsoft.NETFramework.ReferenceAssemblies
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: Xunit.SkippableFact
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

BitFaster.Caching.UnitTests.Std/BitFaster.Caching.UnitTests.Std.csproj

@@ -19,7 +19,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.5.23" />
   </ItemGroup>
 
   <ItemGroup>

BitFaster.Caching.UnitTests/BitFaster.Caching.UnitTests.csproj

@@ -19,7 +19,7 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="Xunit.SkippableFact" Version="1.4.13" />
+    <PackageReference Include="Xunit.SkippableFact" Version="1.5.23" />
   </ItemGroup>
 
   <ItemGroup Condition="'$(TargetFramework)' == 'net48'">