ci.yml: set actions/checkout version

Author: Sergey Khomushin

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@main
+      - uses: actions/checkout@v3
 
       - name: Install modules
         run: npm ci