Revert "Bump codecov/codecov-action from 3 to 4"

Author: BenjaminRemez

.github/workflows/CI.yml

@@ -40,7 +40,7 @@ jobs:
       - uses: julia-actions/julia-buildpkg@v1
       - uses: julia-actions/julia-runtest@v1
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v4
+      - uses: codecov/codecov-action@v3
         with:
           files: lcov.info
   docs: