ci: Update to actions/checkout@v4.

Author: waywardmonkeys

.github/workflows/main.yml

@@ -26,7 +26,7 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install packages for fuzzing
         if: runner.os == 'Linux' && matrix.fuzz == 1