Update extractions/setup-just action to v3 (#39690)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [extractions/setup-just](https://redirect.github.com/extractions/setup-just) | action | major | `v2` -> `v3` |

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### Release Notes

<details>
<summary>extractions/setup-just (extractions/setup-just)</summary>

### [`v3`](https://redirect.github.com/extractions/setup-just/compare/v2...v3)

[Compare Source](https://redirect.github.com/extractions/setup-just/compare/v2...v3)

</details>

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### Configuration

📅 **Schedule**: Branch creation - "on the first day of the month" in timezone America/Los_Angeles, Automerge - 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.

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 - [ ] If you want to rebase/retry this PR, check this box

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This PR has been generated by [Renovate Bot](https://redirect.github.com/renovatebot/renovate).

GitOrigin-RevId: 80ced52a9d34b2efd2cd7372c4c87854c0383015

Author: convex-renovate-runner[bot]

.github/actions/setup-rust/action.yml

@@ -20,7 +20,7 @@ runs:
       run: sudo apt-get install pkg-config libsodium-dev libssl-dev
 
     - name: Install Just
-      uses: extractions/setup-just@v2
+      uses: extractions/setup-just@v3
       env:
         GITHUB_TOKEN: ${{ inputs.github-token }}