System.Text.Json source generation sample does not work anymore

### Type of issue

Code doesn't work

### Description

### Page URL

https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/source-generation

### Content source URL

https://github.com/dotnet/docs/blob/main/docs/standard/serialization/system-text-json/source-generation.md

### Document Version Independent Id

558903e9-8173-464e-ff8b-7744419ad7e4

### Platform Id

5625b9f7-1115-e464-d692-07331c891523

### Article author

@gewarren

### Metadata

* ID: ee53c3dc-df79-82ef-ce25-3233ff292c55
* PlatformId: 5625b9f7-1115-e464-d692-07331c891523
* Service: **dotnet-fundamentals**

[Related Issues](https://github.com/dotnet/docs/issues?q=is%3Aissue+is%3Aopen+558903e9-8173-464e-ff8b-7744419ad7e4)

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[Associated WorkItem - 558443](https://dev.azure.com/msft-skilling/Content/_workitems/edit/558443)