regenerate for schema changes by 2022-12-28

Done with:

	GITHUB_TOKEN=<redacted> go generate ./...

Add special handling of the SponsorsCountryOrRegionCode enum to gen.go
to generate better identifier names. I'm not sure if including them at
all is very useful, but do it anyway to avoid the surprise of just one
enum not having its values available.

Reference: https://docs.github.com/en/graphql/overview/changelog.

Closes https://github.com/shurcooL/githubv4/pull/112.

Co-authored-by: Sean Smith <sean@wwsean08.com>