Update actions/checkout action to v6

Author: renovate[bot]

.github/workflows/cmake.yml

@@ -17,7 +17,7 @@ jobs:
           - os: macos-latest
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - uses: actions/setup-python@v6
     - run: |
         pipx install conan