fix: samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Org.OpenAPITools.csproj to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-DOTNET-SYSTEMTEXTJSON-8168848

Author: snyk-bot

samples/server/petstore/aspnetcore-6.0-nullableReferenceTypes/src/Org.OpenAPITools/Org.OpenAPITools.csproj

@@ -15,7 +15,7 @@
         <DockerfileContext>..\..</DockerfileContext>
     </PropertyGroup>
     <ItemGroup>
-        <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="6.0.0" />
+        <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="7.0.0" />
         <PackageReference Include="Microsoft.VisualStudio.Azure.Containers.Tools.Targets" Version="1.10.8" />
         <PackageReference Include="Swashbuckle.AspNetCore.Newtonsoft" Version="6.4.0" />
         <PackageReference Include="Swashbuckle.AspNetCore.SwaggerUI" Version="6.4.0" />