workflow: Bump actions/checkout to v4

Author: sudotac

.github/workflows/vader.yml

@@ -12,17 +12,17 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Git clone Vader
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: junegunn/vader.vim
           path: vader.vim
       - name: Git clone Fugitive
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           repository: tpope/vim-fugitive
           path: vim-fugitive
       - name: Check out repository code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
         with:
           path: fugitive-cgit.vim
       - name: Install packages