update actions/checkout in GitHub Actions to v3 (#51)

Author: striezel

.github/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Install GCC ${{ matrix.version }}
         run: sudo apt-get install -y gcc-${{ matrix.version }} g++-${{ matrix.version }}
@@ -50,7 +50,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Install Clang ${{ matrix.version }}
         run: sudo apt-get install -y clang-${{ matrix.version }}
@@ -80,7 +80,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
 
       - name: Configure tests
         run: cmake -S . -B build