deps: update actions/github-script action to v5 (#1658)

[![WhiteSource Renovate](https://app.renovatebot.com/images/banner.svg)](https://renovatebot.com)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/github-script](https://togithub.com/actions/github-script) | action | major | `v3` -> `v5` |

---

### Release Notes

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

### [`v5`](https://togithub.com/actions/github-script/compare/v4...v5)

[Compare Source](https://togithub.com/actions/github-script/compare/v4...v5)

### [`v4`](https://togithub.com/actions/github-script/compare/v3...v4)

[Compare Source](https://togithub.com/actions/github-script/compare/v3...v4)

</details>

---

### Configuration

📅 **Schedule**: At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, click this checkbox.

---

This PR has been generated by [WhiteSource Renovate](https://renovate.whitesourcesoftware.com). View repository job log [here](https://app.renovatebot.com/dashboard#github/googleapis/java-spanner).