/// <summary>
 /// Sets the Content-Type header of the request to the specified media type.
 /// </summary>
 /// <param name="mediaType">The Content-Type header media type.</param>
 /// <returns>An <see cref="IRequest"/> object that represents the request.</returns>
 public static IRequest ContentType(this IWith @this, string mediaType)
 => @this.ContentType(new MediaTypeHeaderValue(mediaType));