Bump Microsoft.OpenApi.Readers from 1.6.20 to 1.6.21

Bumps [Microsoft.OpenApi.Readers](https://github.com/Microsoft/OpenAPI.NET) from 1.6.20 to 1.6.21.
- [Release notes](https://github.com/Microsoft/OpenAPI.NET/releases)
- [Commits](microsoft/OpenAPI.NET@1.6.20...1.6.21)

---
updated-dependencies:
- dependency-name: Microsoft.OpenApi.Readers
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

src/lib/apimanifest.csproj

@@ -30,7 +30,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.OpenApi.Readers" Version="1.6.20" />
+    <PackageReference Include="Microsoft.OpenApi.Readers" Version="1.6.21" />
     <PackageReference Include="Microsoft.VisualStudio.Threading.Analyzers" Version="17.11.20">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>