chore(deps): update dependency pytest to v5.4.1 (#3189)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [pytest](https://docs.pytest.org/en/latest/) | minor | `==5.3.2` -> `==5.4.1` |

---

### Renovate configuration

:date: **Schedule**: At any time (no schedule defined).

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

:recycle: **Rebasing**: Never, or you tick the rebase/retry checkbox.

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

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [WhiteSource Renovate](https://renovate.whitesourcesoftware.com). View repository job log [here](https://app.renovatebot.com/dashboard#GoogleCloudPlatform/python-docs-samples).

Author: renovate-bot

run/system-package/requirements.txt

@@ -1,3 +1,3 @@
 Flask==1.1.1
-pytest==5.3.2
+pytest==5.4.1
 gunicorn==20.0.4