chore(deps): update actions/checkout action to v6 (#345)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | major | `v4` -> `v6` |

---

### Release Notes

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

### [`v6`](https://redirect.github.com/actions/checkout/compare/v5...v6)

[Compare
Source](https://redirect.github.com/actions/checkout/compare/v5...v6)

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

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

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined),
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

---

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.github/workflows/ci.yml

@@ -26,7 +26,7 @@ jobs:
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
 
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - uses: actions-rs/toolchain@v1
         with:
@@ -70,7 +70,7 @@ jobs:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
 
       - name: checkout source
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Rust stable toolchain
         uses: actions-rs/toolchain@v1
@@ -106,7 +106,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install nightly toolchain
         uses: actions-rs/toolchain@v1
@@ -132,7 +132,7 @@ jobs:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Checkout sources
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install stable toolchain
         uses: actions-rs/toolchain@v1

.github/workflows/docs.yml

@@ -15,7 +15,7 @@ jobs:
           repo-token: ${{ secrets.GITHUB_TOKEN }}
 
       - name: Checkout sources
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install stable toolchain
         uses: actions-rs/toolchain@v1