Bump GitHub checkout action to v6, nonstd-lite isuue 85

nonstd-lite/nonstd-lite#85

Author: martinmoene

.github/workflows/ci.yml

@@ -58,7 +58,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install Clang ${{ matrix.version }}
         run: sudo apt-get install -y clang-${{ matrix.version }}