deps(actions): bump codecov/codecov-action from 5 to 6

Bumps [codecov/codecov-action](https://github.com/codecov/codecov-action) from 5 to 6.
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@v5...v6)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

.github/workflows/stack-tests.yml

@@ -64,7 +64,7 @@ jobs:
             --cov-report=xml --cov-report=term
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         if: always()
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
@@ -96,7 +96,7 @@ jobs:
         run: npm run test:coverage
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           files: frontend/coverage/lcov.info
@@ -262,7 +262,7 @@ jobs:
         run: docker compose cp backend:/app/coverage-e2e.xml backend/coverage-e2e.xml || true
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         if: always()
         with:
           token: ${{ secrets.CODECOV_TOKEN }}