Installation field is missing in CodeScanningAlertEvent type

[LuBingtan]

According to the description about code_scanning_alert event on github api doc, code_scanning_alert event payload should contain the installation field.

But currently it is missing:

go-github/github/event_types.go

Lines 1382 to 1392 in 4a5aa8c

	// GitHub API docs: https://docs.github.com/en/developers/webhooks-and-events/webhooks/webhook-events-and-payloads#code_scanning_alert
	type CodeScanningAlertEvent struct {
	Action *string `json:"action,omitempty"`
	Alert *Alert `json:"alert,omitempty"`
	Ref *string `json:"ref,omitempty"`
	// CommitOID is the commit SHA of the code scanning alert
	CommitOID *string `json:"commit_oid,omitempty"`
	Repo *Repository `json:"repository,omitempty"`
	Org *Organization `json:"organization,omitempty"`
	Sender *User `json:"sender,omitempty"`
	}