Upgrade checkout action from v3 to v4

Author: sych74

.github/workflows/main.yml

@@ -9,7 +9,7 @@ jobs:
 
     steps:
     - name: Checkout code
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Set up Go
       uses: actions/setup-go@v4