chore(deps): update dependency pyopenssl to v21 (GoogleCloudPlatform#6759)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [pyopenssl](https://pyopenssl.org/) | `==20.0.1` -> `==21.0.0` | [![age](https://badges.renovateapi.com/packages/pypi/pyopenssl/21.0.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/pyopenssl/21.0.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/pyopenssl/21.0.0/compatibility-slim/20.0.1)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/pyopenssl/21.0.0/confidence-slim/20.0.1)](https://docs.renovatebot.com/merge-confidence/) |

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cloud-sql/sql-server/sqlalchemy/requirements.txt

@@ -2,6 +2,6 @@ Flask==2.0.1
 SQLAlchemy==1.4.22
 python-tds==1.11.0
 sqlalchemy-pytds==0.3.3
-pyopenssl==20.0.1
+pyopenssl==21.0.0