Update .github/workflows/ci.yml

Author: hattya

.github/workflows/ci.yml

@@ -38,9 +38,9 @@ jobs:
     timeout-minutes: 10
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
       - name: Checkout themis.vim
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: thinca/vim-themis
           path: vim-themis