It seems not possible anymore to use a hyphen in a MySQL database name (like "joomla-cms").

Steps to reproduce the issue

Install Joomla and use a database name with a hyphen in the name, for example joomla-cms

Expected result

In Joomla 3.x you could use a hyphen in the database name.
I would expect to do the same in Joomla 4.

Actual result

Trying to use a MySQL database called "joomla-cms" resulted in the following warning:
The database name is invalid. It must start with a letter, followed by alphanumeric characters.

A workaround is to use an underscore instead, like joomla-cms

System information (as much as possible)

Joomla 4.0-dev
PHP 7.2.17-1
MySQL 5.5.5-10.1.37-MariaDB-0+deb9u1