Improve CI configuration
CHANGELOG:
### Fixed
- [#472](https://gitlab.com/coopdevs/odoo-somconnexio/-/merge_requests/472) Improve the CI:
- Verify the Codecov Bash upload script integrity.
- Add job to check if coverage decrease from a minimun configured.
- Verify the Codecov Bash upload script integrity.
More info in https://about.codecov.io/security-update/
- Add job to check if coverage decrease from a minimum configured.
Following the next article: https://rpadovani.com/gitlab-code-coverage
Edited by Pelayo García