Update GH codecov action to v6

Author: norkans7

.github/workflows/ci.yml

@@ -1,7 +1,5 @@
 name: CI
 on: [push, pull_request]
-env:
-  FORCE_JAVASCRIPT_ACTIONS_TO_NODE24 : true
 jobs:
   test:
     name: Test
@@ -38,7 +36,7 @@ jobs:
 
       - name: Upload coverage
         if: success()
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           fail_ci_if_error: true