ci: bump actions/checkout from 5 to 6 (#316)

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...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/cmake.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     name: ${{ matrix.os }} - shared=${{ matrix.shared }}
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Build
       run: |
         mkdir build
@@ -60,7 +60,7 @@ jobs:
       run:
         shell: msys2 {0}
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: msys2/setup-msys2@v2
       with:
         install: gcc make mingw-w64-x86_64-cmake

.github/workflows/make.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     name: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     # TODO: update makefile to check MANIFEST
     - name: Install dependencies (MacOS)
       if: runner.os == 'macOS'