Update codecov/codecov-action action to v4 (#168)

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This PR contains the following updates:

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

---

### Release Notes

<details>
<summary>codecov/codecov-action (codecov/codecov-action)</summary>

### [`v4`](https://togithub.com/codecov/codecov-action/compare/v3...v4)

[Compare
Source](https://togithub.com/codecov/codecov-action/compare/v3...v4)

</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/test.yml

@@ -49,7 +49,7 @@ jobs:
           tox -e py
 
       - name: Upload coverage
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           flags: ${{ matrix.os }}
           name: ${{ matrix.os }} Python ${{ matrix.python-version }}