chore(deps): Update actions/checkout action to v6 (#392)

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/blob/HEAD/CHANGELOG.md#v600)

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

-   Persist creds to a separate file by [@&#8203;ericsciple](https://redirect.github.com/ericsciple) in [https://github.com/actions/checkout/pull/2286](https://redirect.github.com/actions/checkout/pull/2286)
-   Update README to include Node.js 24 support details and requirements by [@&#8203;salmanmkc](https://redirect.github.com/salmanmkc) in [https://github.com/actions/checkout/pull/2248](https://redirect.github.com/actions/checkout/pull/2248)

</details>

---

### Configuration

📅 **Schedule**: Branch creation - Between 12:00 AM and 03:59 AM, on day 1 of the month ( * 0-3 1 * * ) (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

---

This PR has been generated by [Renovate Bot](https://redirect.github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0MC4yMi4xIiwidXBkYXRlZEluVmVyIjoiNDAuMjIuMSIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOltdfQ==-->

Author: cq-bot

.github/workflows/lint_golang.yml

@@ -15,7 +15,7 @@ jobs:
     name: Lint with GolangCI
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: actions/setup-go@v6
         with:
           go-version-file: go.mod

.github/workflows/lint_markdown.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Vale
         uses: errata-ai/vale-action@v2
         with:
@@ -26,7 +26,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Git checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: markdownlint-cli
         uses: nosborn/github-action-markdown-cli@v3.5.0
         with:

.github/workflows/unittest.yml

@@ -23,7 +23,7 @@ jobs:
           git config --global core.autocrlf false
           git config --global core.eol lf
       - name: Check out code into the Go module directory
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up Go 1.x
         uses: actions/setup-go@v6
         with: