Use multiple target frameworks.

[maliming]

Resolve #16430

We can use the below code to use different features.

#if NET7_0
        var client = new HttpClient();
        client.DefaultRequestVersion = HttpVersion.Version20;
#elif NETSTANDARD2_1
        var client = new HttpClient();
#elif NETSTANDARD2_0
        var client = new HttpClient();
#endif

[applebananamilk]

Whether to test against multiple frameworks?