deps: update dependency requests to v2.28.1 (#902)

[![Mend Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [requests](https://requests.readthedocs.io) ([source](https://togithub.com/psf/requests), [changelog](https://togithub.com/psf/requests/blob/master/HISTORY.md)) | `==2.27.1` -> `==2.28.1` | [![age](https://badges.renovateapi.com/packages/pypi/requests/2.28.1/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/requests/2.28.1/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/requests/2.28.1/compatibility-slim/2.27.1)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/requests/2.28.1/confidence-slim/2.27.1)](https://docs.renovatebot.com/merge-confidence/) |

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Renovate will not automatically rebase this PR, because other commits have been found.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, click this checkbox. ⚠ **Warning**: custom changes will be lost.

---

This PR has been generated by [Mend Renovate](https://www.mend.io/free-developer-tools/renovate/). View repository job log [here](https://app.renovatebot.com/dashboard#github/googleapis/java-document-ai).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiIzMi4yMDYuMCIsInVwZGF0ZWRJblZlciI6IjMyLjIwNi4wIn0=-->