CI: Update actions/checkout to v4.

.github/workflows/deps-test.yml

@@ -13,11 +13,11 @@ jobs:
         shell: cmd
     steps:
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
       with:
         path: megasource
     - name: Checkout LÖVE
-      uses: actions/checkout@v2
+      uses: actions/checkout@v4
       with:
         path: megasource/libs/love
         repository: love2d/love