Bump cache action to v4

Author: thirtythreeforty

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
     steps:
     - uses: actions/checkout@v2
     - name: Cache downloads
-      uses: actions/cache@v1
+      uses: actions/cache@v4
       with:
         path: dl/
         key: dl