Sync default issue closing pattern in doc and implementation

**What does this PR do?**
This PR fixes the differences in the default pattern for closing an issue through the commit message. The configuration file supposes an an default issue pattern different than the actual implementation.

**Are there points in the code the reviewer needs to double check?**
Compare the `gitlab.yml` the the initializers.

**What are the relevant issue numbers / Feature requests?**
This fixes #6742