chore(deps): bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v4...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
     name: Lint
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 22
@@ -27,7 +27,7 @@ jobs:
     name: Security Audit
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 22
@@ -45,7 +45,7 @@ jobs:
       matrix:
         node-version: [20, 22]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node-version }}
@@ -64,7 +64,7 @@ jobs:
       JWT_SECRET: ci-test-secret-with-sufficient-length-for-validation
       API_KEY_SECRET: ci-test-api-key-secret-long
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: ${{ matrix.node-version }}
@@ -80,7 +80,7 @@ jobs:
       JWT_SECRET: ci-test-secret-with-sufficient-length-for-validation
       API_KEY_SECRET: ci-test-api-key-secret-long
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 22
@@ -99,7 +99,7 @@ jobs:
       JWT_SECRET: ci-test-secret-with-sufficient-length-for-validation
       API_KEY_SECRET: ci-test-api-key-secret-long
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - uses: actions/setup-node@v6
         with:
           node-version: 22

.github/workflows/docker-publish.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Extract version from release tag
         id: version

.github/workflows/npm-publish.yml

@@ -14,7 +14,7 @@ jobs:
     environment: NPM_TOKEN
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup Node.js
         uses: actions/setup-node@v6