Convert to ESM.

Context: https://github.com/actions/typescript-action/pull/969

__fixtures__/github.ts

@@ -0,0 +1,15 @@
+import * as github from '@actions/github'
+import { jest } from '@jest/globals'
+
+export const context = {
+  repo: {
+    owner: 'test-owner',
+    repo: 'test-repo'
+  },
+  sha: 'test-sha',
+  ref: 'test-ref',
+  workflow: 'test-workflow',
+  job: 'test-job',
+  runId: '12345'
+}
+export const getOctokit = jest.fn<typeof github.getOctokit>()