[Schema Inaccuracy] head.label and head.user can be null in pull-request schema

[bigfootjon]

Schema Inaccuracy
The current schema for #/components/schemas/pull-request defines head.label and head.user as required.

Expected
head.label and head.user should have nullable: true with the nullability conditions documented (from what I understand, if the user's account was deleted for some reason: all the cases I can see are for "ghost" users)

Reproduction Steps
❯ curl -s https://api.github.com/repos/odoo/odoo/pulls/51976 | jq .head
{
"label": null,
"ref": "12.0",
"sha": "3cf7aba2e293417c6e8a6a4785624c8315ccbb7a",
"user": null,
"repo": null
}
Side-note
The same issue was fixed for head.repo as reported in #161 and #424, would be nice to also add a description to that property explaining the conditions under which it can be null.

[bigfootjon]

This was previously filed as #916

[nickfloyd]

Thanks for submitting an issue! I've routed this internal to the team that owns the endpoint so it can be addressed.