ci: Update to actions/checkout@v4. (#321)

Author: waywardmonkeys

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
             env:
               DO_FUZZ: 1
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - name: Install packages
         if: matrix.os == 'ubuntu-latest'