chore(deps): update dependency google-api-core to v1.24.0 (#709)

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This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [google-api-core](https://togithub.com/googleapis/python-api-core) | minor | `==1.23.0` -> `==1.24.0` |

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### Release Notes

<details>
<summary>googleapis/python-api-core</summary>

### [`v1.24.0`](https://togithub.com/googleapis/python-api-core/blob/master/CHANGELOG.md#&#8203;1240-httpswwwgithubcomgoogleapispython-api-corecomparev1230v1240-2020-12-14)

[Compare Source](https://togithub.com/googleapis/python-api-core/compare/v1.23.0...v1.24.0)

##### Features

-   add support for Python 3.9, drop support for Python 3.5 ([#&#8203;111](https://www.github.com/googleapis/python-api-core/issues/111)) ([fdbed0f](https://www.github.com/googleapis/python-api-core/commit/fdbed0f0cbae8de21c73338a6817f8aa79cef4c9)), closes [#&#8203;110](https://www.github.com/googleapis/python-api-core/issues/110)

##### Documentation

-   explain how to create credentials from dict ([#&#8203;109](https://www.github.com/googleapis/python-api-core/issues/109)) ([5dce6d6](https://www.github.com/googleapis/python-api-core/commit/5dce6d61e7324a415c1b3ceaeec1ce1b5f1ea189))

</details>

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requirements.txt

@@ -1,5 +1,5 @@
 click==7.1.2
-google-api-core==1.23.0
+google-api-core==1.24.0
 googleapis-common-protos==1.52.0
 jinja2==2.11.2
 MarkupSafe==1.1.1