Update actions/checkout to v4 in ci.yml

Author: linjunpop

.github/workflows/ci.yml

@@ -31,7 +31,7 @@ jobs:
             elixir: "1.17.0"
     steps:
       - name: Checkout source code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Setup OTP and Elixir
         uses: erlef/setup-beam@v1
         with: