Update GitHub actions to v4 (major) (#123)

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This PR contains the following updates:

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

---

### Release Notes

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

###
[`v4`](https://togithub.com/actions/checkout/blob/HEAD/CHANGELOG.md#v417)

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

- Bump the minor-npm-dependencies group across 1 directory with 4
updates by [@&#8203;dependabot](https://togithub.com/dependabot) in
[https://github.com/actions/checkout/pull/1739](https://togithub.com/actions/checkout/pull/1739)
- Bump actions/checkout from 3 to 4 by
[@&#8203;dependabot](https://togithub.com/dependabot) in
[https://github.com/actions/checkout/pull/1697](https://togithub.com/actions/checkout/pull/1697)
- Check out other refs/\* by commit by
[@&#8203;orhantoy](https://togithub.com/orhantoy) in
[https://github.com/actions/checkout/pull/1774](https://togithub.com/actions/checkout/pull/1774)
- Pin actions/checkout's own workflows to a known, good, stable version.
by [@&#8203;jww3](https://togithub.com/jww3) in
[https://github.com/actions/checkout/pull/1776](https://togithub.com/actions/checkout/pull/1776)

</details>

<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>

---

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---

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---

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.github/workflows/ci.yaml

@@ -20,7 +20,7 @@ jobs:
     timeout-minutes: 5
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Install tox & poetry
         run: |
           pipx install tox
@@ -34,23 +34,23 @@ jobs:
     timeout-minutes: 5
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Install tox & poetry
         run: |
           pipx install tox
           pipx install poetry
       - name: Run tests
         run: tox run -e unit
       - name: Upload Coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
 
   lib-check:
     name: Check libraries
     runs-on: ubuntu-latest
     timeout-minutes: 5
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           fetch-depth: 0
       - run: |
@@ -83,7 +83,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Install tox & poetry
         run: |
           pipx install tox
@@ -137,7 +137,7 @@ jobs:
     timeout-minutes: 120
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Install tox & poetry
         run: |
           pipx install tox