chore(deps): update actions/checkout action to v6 (#161)

This PR contains the following updates:

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

</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 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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View the [repository job
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.github/workflows/black.yaml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         ref: ${{ github.head_ref }}  # Check out the PR branch
 

.github/workflows/compile.yaml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           # Check out the PR branch
           ref: ${{ github.head_ref }}

.github/workflows/deploy-docs.yaml

@@ -22,7 +22,7 @@ jobs:
       name: github-pages
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
 
@@ -52,7 +52,7 @@ jobs:
           publish_dir: ./docs/_build/html
 
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: gh-pages
           persist-credentials: false

.github/workflows/mypy.yaml

@@ -24,7 +24,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         fetch-depth: 0
         persist-credentials: false

.github/workflows/pytest.yaml

@@ -42,7 +42,7 @@ jobs:
 
     steps:
       - name: Check out repository code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           persist-credentials: false
 

.github/workflows/release.yaml

@@ -79,7 +79,7 @@ jobs:
 
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 
@@ -117,7 +117,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0