build(deps): 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/main.yml

@@ -105,7 +105,7 @@ jobs:
         run: make -C backend docs
 
       - name: Upload backend coverage reports to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           flags: backend
           directory: backend
@@ -161,7 +161,7 @@ jobs:
         run: make -C frontend test-ci
 
       - name: Upload frontend coverage reports to Codecov
-        uses: codecov/codecov-action@v5
+        uses: codecov/codecov-action@v6
         with:
           flags: frontend
           directory: frontend