[BUG] [csharp] Obsolete build warnings after PR to update to RestSharp 112.0.0

[johnthagen]

Bug Report Checklist

• [ ] Have you provided a full/minimal spec to reproduce the issue?
• [ ] Have you validated the input using an OpenAPI validator (example)?
• [ ] Have you tested with the latest master to confirm the issue still exists?
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Description

Due to vulnerabilities in the current generated RestSharp version

• 19387

I tried to update 7.8.0 generated C# client to RestSharp 112.0.0 as shown in

• 19507

But this produced two build warnings. For projects that treat warnings as errors in CI, this will fail the build.

ApiClient.cs(400,17): warning CS0618: 'RestClientOptions.MaxTimeout' is obsolete: 'Use Timeout instead.'
ApiClient.cs(472,24): warning CS0618: 'RestClientExtensions.Deserialize<T>(IRestClient, RestResponse)' is obsolete: 'Please use the async overload with a cancellation token'

The related upstream changes in RestSharp:

• https://github.com/restsharp/RestSharp/pull/2228
• https://github.com/restsharp/RestSharp/pull/2078
• https://github.com/restsharp/RestSharp/pull/2141

Here are where these obsolete methods are still used within openapi-generator main branch:

https://github.com/OpenAPITools/openapi-generator/blob/e914c4098b44ac734d3dd21300d433f6cb2974a5/modules/openapi-generator/src/main/resources/csharp/ApiClient.mustache#L458

https://github.com/OpenAPITools/openapi-generator/blob/e914c4098b44ac734d3dd21300d433f6cb2974a5/modules/openapi-generator/src/main/resources/csharp/ApiClient.mustache#L557

openapi-generator version

7.8.0 (with #19507 backport manually applied)

[johnthagen]

CC @wing328

[alec-petersen]

Got a fix for this issue in review #19847