Issue Number does not populate correctly in `@actions/github` Context.issue

[thboop]

Describe the bug
Issue number is empty for PullRequestReview and PullRequestReviewComment events

To Reproduce

1. Create an action using the following ts file:

import * as core from '@actions/core'
import * as github from '@actions/github'

async function run(): Promise<void> {
  try {
    core.info(`Issue number is: ${JSON.stringify(github.context.issue.number)}`)
  } catch (error) {
    core.setFailed(error.message)
  }
}

run()

2. Setup the workflow to run on on: [pull_request_review, pull_request_review_comment]
3. Create a PR with a linked issue

Expected behavior
The Issue number field should be populated.

Screenshots
The issue number field is null.

Additional context
We appear to be accessing pullRequest instead of pull_request causing this bug:
https://github.com/actions/toolkit/blob/master/packages/github/src/context.ts#L47