Update mheap/github-action-required-labels action to v4 (#37)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
|
[mheap/github-action-required-labels](https://togithub.com/mheap/github-action-required-labels)
| action | major | `v3` -> `v4` |

---

### Release Notes

<details>
<summary>mheap/github-action-required-labels</summary>

###
[`v4`](https://togithub.com/mheap/github-action-required-labels/releases/tag/v4)

[Compare
Source](https://togithub.com/mheap/github-action-required-labels/compare/v3...v4)

Tag that always points to the latest commit in the v4.x.x series of
releases

</details>

---

### Configuration

📅 **Schedule**: Branch creation - "on the first day of the month" (UTC),
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.

---

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

---

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.github/workflows/require-pr-label.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: mheap/github-action-required-labels@v3
+      - uses: mheap/github-action-required-labels@v4
         with:
           mode: minimum
           count: 1