chore(deps): update dependency google-cloud-kms to v2.4.0 (#135)

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This PR contains the following updates:

| Package | Change | Age | Adoption | Passing | Confidence |
|---|---|---|---|---|---|
| [google-cloud-kms](https://togithub.com/googleapis/python-kms) | `==2.3.0` -> `==2.4.0` | [![age](https://badges.renovateapi.com/packages/pypi/google-cloud-kms/2.4.0/age-slim)](https://docs.renovatebot.com/merge-confidence/) | [![adoption](https://badges.renovateapi.com/packages/pypi/google-cloud-kms/2.4.0/adoption-slim)](https://docs.renovatebot.com/merge-confidence/) | [![passing](https://badges.renovateapi.com/packages/pypi/google-cloud-kms/2.4.0/compatibility-slim/2.3.0)](https://docs.renovatebot.com/merge-confidence/) | [![confidence](https://badges.renovateapi.com/packages/pypi/google-cloud-kms/2.4.0/confidence-slim/2.3.0)](https://docs.renovatebot.com/merge-confidence/) |

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### Release Notes

<details>
<summary>googleapis/python-kms</summary>

### [`v2.4.0`](https://togithub.com/googleapis/python-kms/blob/master/CHANGELOG.md#&#8203;240-httpswwwgithubcomgoogleapispython-kmscomparev230v240-2021-07-12)

[Compare Source](https://togithub.com/googleapis/python-kms/compare/v2.3.0...v2.4.0)

##### Features

-   add always_use_jwt_access ([#&#8203;129](https://www.github.com/googleapis/python-kms/issues/129)) ([cfa0802](https://www.github.com/googleapis/python-kms/commit/cfa08022db3e096e2414418b63482606af8d46cb))

##### Bug Fixes

-   disable always_use_jwt_access ([#&#8203;133](https://www.github.com/googleapis/python-kms/issues/133)) ([8007b81](https://www.github.com/googleapis/python-kms/commit/8007b810f11ebf49cd24edd77867abac174841e9))

##### Documentation

-   Include verify_attestation_chains.py help text to attestations README ([#&#8203;134](https://www.github.com/googleapis/python-kms/issues/134)) ([2f2bb49](https://www.github.com/googleapis/python-kms/commit/2f2bb49adca244031d584ffbb27e32585e64ed42))
-   omit mention of Python 2.7 in 'CONTRIBUTING.rst' ([#&#8203;1127](https://www.github.com/googleapis/python-kms/issues/1127)) ([#&#8203;124](https://www.github.com/googleapis/python-kms/issues/124)) ([5c3e273](https://www.github.com/googleapis/python-kms/commit/5c3e27391c4771b4a03c87e21a5260ed8d61b9c4)), closes [#&#8203;1126](https://www.github.com/googleapis/python-kms/issues/1126)

</details>

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kms/snippets/requirements.txt

@@ -1,3 +1,3 @@
-google-cloud-kms==2.3.0
+google-cloud-kms==2.4.0
 cryptography==3.4.7
 crcmod==1.7