Sonar: Use concise character class syntax '\d' instead of '[0-9]'

[qmonmert]

Fix https://sonarcloud.io/project/issues?resolved=false&severities=MINOR&types=CODE_SMELL&id=jhipster-sample-application&open=AYEG0QoT0HaWLliKRoX_

---

Please make sure the below checklist is followed for Pull Requests.

• All continuous integration tests are green
• Tests are added where necessary
• The JDL part is updated if necessary
• jhipster-online is updated if necessary
• Documentation is added/updated where necessary
• Coding Rules & Commit Guidelines as per our CONTRIBUTING.md document are followed

When you are still working on the PR, consider converting it to Draft (below reviewers) and adding skip-ci label, you can still see CI build result at your branch.