Bump actions/checkout from 4 to 6 (#208)

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](actions/checkout@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>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: deps
         run: |
@@ -44,7 +44,7 @@ jobs:
           compiler: { CC: "gcc", CXX: "g++" }
     runs-on: ${{ matrix.platform }}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: 'true'
     - name: Install ICU (Ubuntu)
@@ -97,7 +97,7 @@ jobs:
           - "3.11"
     runs-on: ${{ matrix.platform }}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.python }}
@@ -134,7 +134,7 @@ jobs:
         build-shared: ["0", "1"]
     runs-on: windows-2019
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
       with:
         submodules: 'true'
     - name: Enable ASan Sanitizers
@@ -179,7 +179,7 @@ jobs:
           - "3.11"
     runs-on: windows-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
     - uses: actions/setup-python@v6
       with:
         python-version: ${{ matrix.python }}

.github/workflows/release.yml

@@ -10,7 +10,7 @@ jobs:
     name: upload release to PyPI
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - uses: actions/setup-python@v6
       with: