chore(deps): update actions/checkout action to v5 (#995)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | major | `v4` -> `v5` |

---

### Release Notes

<details>
<summary>actions/checkout (actions/checkout)</summary>

### [`v5`](https://redirect.github.com/actions/checkout/compare/v4...v5)

[Compare
Source](https://redirect.github.com/actions/checkout/compare/v4...v5)

</details>

---

### Configuration

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Automerge - At any time (no schedule defined).

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

♻ **Rebasing**: Whenever PR is behind base branch, 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, check
this box

---

This PR was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/launchdarkly/js-core).

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<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Update `actions/checkout` from v4 to pinned v5 in the
`release-shopify-oxygen` job of `.github/workflows/release-please.yml`.
> 
> - **CI/CD (GitHub Actions)**:
> - In `.github/workflows/release-please.yml`, update `actions/checkout`
from `v4` to pinned `v5` (`08c6903...`) for the `release-shopify-oxygen`
job.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
95a565c. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/release-please.yml

@@ -533,7 +533,7 @@ jobs:
       contents: write
     if: ${{ always() && !failure() && !cancelled() && needs.release-please.outputs.package-sdk-shopify-oxygen-released == 'true'}}
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5
       - uses: actions/setup-node@2028fbc5c25fe9cf00d9f06a71cc4710d4507903 # v6
         with:
           node-version: 24.x