catch error if pr has already been created

[Somberland]

response:

{"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"A pull request already exists for anfema:p.skorpil/3252-create-basic-routings-for-pool-and-new-sales-system."}],"documentation_url":"https://developer.github.com/v3/pulls/#create-a-pull-request"}
    at /Users/philippskorpil/.config/yarn/global/node_modules/@octokit/rest/lib/request/request.js:72:19
    at processTicksAndRejections (internal/process/task_queues.js:85:5)
    at async module.exports (/Users/philippskorpil/.config/yarn/global/node_modules/work/src/create-pullrequest.js:65:15)
    at async /Users/philippskorpil/.config/yarn/global/node_modules/work/index.js:27:5 {
  name: 'HttpError',
  code: 422,
  status: undefined,
  headers: {
    'access-control-allow-origin': '*',
    'access-control-expose-headers': 'ETag, Link, Location, Retry-After, X-GitHub-OTP, X-RateLimit-Limit, X-RateLimit-Remaining, X-RateLimit-Reset, X-OAuth-Scopes, X-Accepted-OAuth-Scopes, X-Poll-Interval, X-GitHub-Media-Type',
    connection: 'close',
    'content-length': '289',
    'content-security-policy': "default-src 'none'",
    'content-type': 'application/json; charset=utf-8',
    date: 'Mon, 25 Nov 2019 09:32:31 GMT',
    'referrer-policy': 'origin-when-cross-origin, strict-origin-when-cross-origin',
    server: 'GitHub.com',
    status: '422 Unprocessable Entity',
    'strict-transport-security': 'max-age=31536000; includeSubdomains; preload',
    'x-accepted-oauth-scopes': '',
    'x-content-type-options': 'nosniff',
    'x-frame-options': 'deny',
    'x-github-media-type': 'github.v3; format=json',
    'x-github-request-id': 'D9FE:32664:12369D:175BD4:5DDB9FAE',
    'x-oauth-scopes': 'admin:gpg_key, admin:org, admin:org_hook, admin:public_key, admin:repo_hook, gist, notifications, repo, user, write:discussion',
    'x-ratelimit-limit': '5000',
    'x-ratelimit-remaining': '4996',
    'x-ratelimit-reset': '1574677948',
    'x-xss-protection': '1; mode=block'
  }
}