(why) Does a `Repository`'s `language` have to be `serde_json::Value`?

[Stef16Robbe]

First of all, thanks for making this crate! So far it's been great to use.

I just had a small nitpick/question, when retrieving a repository, the primary language has a type of serde_json::Value: https://github.com/XAMPPRocky/octocrab/blob/main/src/models.rs#L751.

I'm questioning whether this is really necessary. I'm listing the starred repo's by the current user and the example response in the GitHub API docs mention that this value can be null or a string:

"language": {
  "type": [
    "string",
    "null"
  ]
},

I also saw that this was not changed since the start of the project (5c1ba26), so maybe this can be revisited? What do you think?

[XAMPPRocky]

Thank you for your issue! This can probably be revisited/changed. I don't remember why it is that way.