Update to version 4 of cache and codecov actions

Author: kostis

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
       - name: Cache .plt directory
-        uses: actions/cache@v3
+        uses: actions/cache@v4
         with:
           path: .plt
           key: ${{ runner.os }}-otp-${{ matrix.otp }}
@@ -75,6 +75,6 @@ jobs:
         env:
           COVER: true
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           files: "_build/test/covertool/proper.covertool.xml"