Integration tests article provides xunit sample when choosing MSTest

### Description

In https://learn.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-9.0, the linked sample appears to be xunit only. The article has an MSTest option at the top though.

### Page URL

https://learn.microsoft.com/en-us/aspnet/core/test/integration-tests?view=aspnetcore-9.0

### Content source URL

https://github.com/dotnet/AspNetCore.Docs/blob/main/aspnetcore/test/integration-tests.md

### Document ID

f499b131-8b14-7e10-1728-543fdd5a5656

### Platform Id

a725fe2a-b11f-6664-eb77-2adc94d55792

### Article author

@tdykstra

### Metadata

* ID: 77889d43-fedb-f8b4-8fea-379ec946555c
* PlatformId: a725fe2a-b11f-6664-eb77-2adc94d55792
* Service: **aspnet-core**
* Sub-service: **testing**

[Related Issues](https://github.com/dotnet/AspNetCore.Docs/issues?q=is%3Aissue+is%3Aopen+f499b131-8b14-7e10-1728-543fdd5a5656)

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