Missing github context `workspace` property

[AArnott]

Describe the bug

The github context's workspace property is not exposed from context.ts:

toolkit/packages/github/src/context.ts

Lines 10 to 20 in 1cc56db

	payload: WebhookPayload
	eventName: string
	sha: string
	ref: string
	workflow: string
	action: string
	actor: string
	job: string
	runNumber: number
	runId: number

Expected behavior

Per the docs I expect to be able to access the workspace property on a github context.