galera_new_cluster.sh ignores service name argument due to hardcoded mariadb.service

In the script galera_new_cluster.sh, the service restart command has been modified from:
`systemctl restart ${1:-mariadb}` to `systemctl restart mariadb.service`.
Related PR: https://github.com/MariaDB/server/pull/4329/changes#diff-c4e1aa182a1b96143d20e9e8e915e27463ab137befa432d7b68f6361e54874d1
This change effectively ignores the optional positional parameter $1, which was previously used to specify a custom service name.
As a result, it is no longer possible to override the service name when invoking the script, breaking previous behavior.

Steps to Reproduce:

• Use a recent MariaDB version
• Run: `galera_new_cluster.sh mariadb-custom.service`
• Observe that the script still executes: `systemctl restart mariadb.service`

Expected Behavior:
The script should respect the optional argument and restart the provided service name, falling back to mariadb if not specified.
https://mariadb.com/docs/galera-cluster/galera-management/installation-and-deployment/getting-started-with-mariadb-galera-cluster#systemd-and-bootstrapping

Additional Information:
This issue surfaced after upgrading MariaDB from 10.11.10 to 10.11.15 via RHEL AppStream.

Proposed Fix:
Restore the previous behavior: `systemctl restart ${1:-mariadb}`

I can submit a pull request to restore the previous behavior if this approach is acceptable.