[BUG][CSHARP] Multiple OAuth Flows generates C# code that doesn't compile

Start with modules/openapi-generator/src/main/resources/csharp/libraries/generichost/DependencyInjectionTests.mustache around line 79, then reproduce the generation command using the linked OpenAPI specification. Verify the generated api-csharp/src/Org.OpenAPITools.Test/Api/DependencyInjectionTests.cs compiles without duplicate OAuthToken declarations.

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator?
• Have you tested with the latest master to confirm the issue still exists?
  • No, but I linked the offending code below and it's still broken in master.
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When you have multiple OAuth flows defined in a specification, the generated C# code fails to compile due to a duplicate variable.

openapi-generator version

7.16.0

OpenAPI declaration file content or url

Example using the stock spec from Swagger Editor. Full spec - https://gist.github.com/scottbusche-usps/9ebaf3038984d40a61a6cf73da87b880

  securitySchemes:
    petstore_auth:
      type: oauth2
      flows:
        clientCredentials:
          tokenUrl: https://petstore3.swagger.io/oauth/token
          scopes:
            "write:pets": modify pets in your account
            "read:pets": read your pets
        implicit:
          authorizationUrl: https://petstore3.swagger.io/oauth/authorize
          scopes:
            "write:pets": modify pets in your account
            "read:pets": read your pets

Generation Details

java -jar openapi-generator-cli.jar generate -g csharp -o api-csharp -i oas.yaml --additional-properties=targetFramework=net8.0

I do not believe it matters on the targetFrameework version.

Steps to reproduce

Try to compile the code generated from the above command. Inside api-csharp/src/Org.OpenAPITools.Test/Api/DependencyInjectionTests.cs will be this block:

        private readonly IHost _hostUsingConfigureWithAClient =
            Host.CreateDefaultBuilder([]).ConfigureApi((context, services, options) =>
            {
                ApiKeyToken apiKeyToken1 = new("<token>", ClientUtils.ApiKeyHeader.Api_key, timeout: TimeSpan.FromSeconds(1));
                options.AddTokens(apiKeyToken1);

                OAuthToken oauthToken = new("token", timeout: TimeSpan.FromSeconds(1));
                options.AddTokens(oauthToken);

                // This oauthToken here has no index and duplicates the first one
                OAuthToken oauthToken = new("token", timeout: TimeSpan.FromSeconds(1));
                options.AddTokens(oauthToken);
                options.AddApiHttpClients(client => client.BaseAddress = new Uri(ClientUtils.BASE_ADDRESS));
            })
            .Build();

Related issues/PRs

Nothing directly related that I could find.

Suggest a fix

This line appears to need to add {{-index}} suffix to the variable name:
https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/csharp/libraries/generichost/DependencyInjectionTests.mustache#L79

This looks pretty straight forward and happy to submit a PR.