Update dependency Microsoft.Kiota.Serialization.Json to 1.21.0 (#42)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

src/Soenneker.Stripe.OpenApiClient.csproj

@@ -44,7 +44,7 @@
     <ItemGroup>
         <PackageReference Include="Microsoft.Kiota.Http.HttpClientLibrary" Version="1.21.0" />
         <PackageReference Include="Microsoft.Kiota.Serialization.Form" Version="1.21.0" />
-        <PackageReference Include="Microsoft.Kiota.Serialization.Json" Version="1.20.1" />
+        <PackageReference Include="Microsoft.Kiota.Serialization.Json" Version="1.21.0" />
         <PackageReference Include="Microsoft.Kiota.Serialization.Multipart" Version="1.20.1" />
         <PackageReference Include="Microsoft.Kiota.Serialization.Text" Version="1.20.1" />
     </ItemGroup>