Add text/xml to ContextType of oEmbed response

[Ovis]

Hi.
I'm trying to create a ShortCode that can use oEmbed in a generic way.
Internally, it is assumed to use GetEmbedResultAsync.

During creation, an error occurred when retrieving information from Flickr.
e.g)
Unknown content type for oEmbed response

I checked and found that Flickr's oEmbedAPI specifies text/xml as ContextType.

Statiq.Web/src/Statiq.Web/Shortcodes/EmbedShortcode.cs

Line 99 in d9da990

else if (response.Content.Headers.ContentType.MediaType == MediaTypes.Xml)

GetEmbedResultAsync seems to have an error because it assumes Application/Xml.

Could you please fix this branch to allow text/xml?

e.g.)
https://www.flickr.com/services/oembed/?url=https://www.flickr.com/photos/yuta_arai_0206/8008087593/