deps: update actions/github-script action to v6 (googleapis#716)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/github-script](https://togithub.com/actions/github-script) | action | major | `v5` -> `v6` |

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### Release Notes

<details>
<summary>actions/github-script</summary>

### [`v6`](https://togithub.com/actions/github-script/compare/v5...v6)

[Compare Source](https://togithub.com/actions/github-script/compare/v5...v6)

</details>

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