update actions/cache to v4

Author: cschiewek

.github/workflows/elixir.yml

@@ -35,7 +35,7 @@ jobs:
           elixir-version: ${{matrix.elixir}}
 
       - name: Restore deps cache
-        uses: actions/cache@v2
+        uses: actions/cache@v4
         with:
           path: |
             deps
@@ -61,7 +61,7 @@ jobs:
         run: mix test
 
       - name: Cache/uncache PLTs
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: |
             priv/plts