deps: update dependency google-auth to v2.12.0 (#823)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [google-auth](https://github.com/googleapis/google-auth-library-python) | `==2.11.0` -> `==2.12.0` | [![age](https://badges.renovateapi.com/packages/pypi/google-auth/2.12.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-auth/2.12.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-auth/2.12.0/compatibility-slim/2.11.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-auth/2.12.0/confidence-slim/2.11.0)](https://docs.renovatebot.com/merge-confidence/) |

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