fix: codecov coverage badge (acts-project#3108)

badgen.net not work very stable for codecov and shows `404`. Use instead the badge generated by codecov: https://docs.codecov.com/docs/status-badges

Change from ![badge-old](https://github.com/acts-project/acts/assets/70842573/45d22041-89bf-4a35-84b1-0a87c8627d47) to  ![badge-new](https://github.com/acts-project/acts/assets/70842573/1017f1eb-63aa-41e0-931c-fcc196e975aa)

README.md

@@ -4,7 +4,7 @@ or *A Common Tracking Software* if you do not like recursive acronyms
 
 [![10.5281/zenodo.5141418](https://zenodo.org/badge/DOI/10.5281/zenodo.5141418.svg)](https://doi.org/10.5281/zenodo.5141418)
 [![Chat on Mattermost](https://badgen.net/badge/chat/on%20mattermost/cyan)](https://mattermost.web.cern.ch/acts/)
-[![coverage](https://badgen.net/codecov/c/github/acts-project/acts/main)](https://codecov.io/gh/acts-project/acts/branch/main)
+[![codecov](https://codecov.io/gh/acts-project/acts/branch/master/graph/badge.svg)](https://codecov.io/gh/acts-project/acts)
 [![Latest release](https://badgen.net/github/release/acts-project/acts)](https://github.com/acts-project/acts/releases)
 [![Status](https://badgen.net/github/checks/acts-project/acts/main)](https://github.com/acts-project/acts/actions)
 [![Metrics](https://badgen.net/badge/metric/tracker/purple)](https://acts-project.github.io/metrics/)