fix: add updated_at to graphql query

[trfv]

Summary
fix #4436
add updated_at to graqhql query for pullRequest for editorial workflow card.
without this, moment(entry.get('updatedOn')) will always be Invalid Date.
cf)
/~https://github.com/netlify/netlify-cms/blob/master/packages/netlify-cms-core/src/components/Workflow/WorkflowList.js#L208-L210
/~https://github.com/netlify/netlify-cms/blob/master/packages/netlify-cms-backend-github/src/API.ts#L583

Test plan
e2e test

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[erezrokah]

Thanks @trfv, I'm quite surprised this doesn't break our tests as we use pre-recorded data:
/~https://github.com/netlify/netlify-cms/blob/b94d5f6e7fe07a2816098b377b30a4ddd39c9520/cypress/fixtures/Github%20Backend%20Editorial%20Workflow%20-%20GraphQL%20API__can%20update%20workflow%20status%20from%20within%20the%20editor.json#L376

I'll verify those tests are behaving as they should before merging

[erezrokah]

@trfv, see /~https://github.com/netlify/netlify-cms/pull/5616/files#diff-968c14cc900beced6e94a6fab4c827e18c6c39f9acade8b34fdfdfac2da83fa7R54.

I believe the tests should fail now until we update the relevant snapshots.

[trfv]

@erezrokah
I updated the relevant e2e tests. please check again 🙏 .