Fix Drupal & MySQL 8 installation error

We get the following error on mysql 8, aegir3

Unable to grant privileges to database users. [error]
...
Caught drush error, ending drush_provision_hostmaster_install [error]
Array [error]
(
[PROVISION_GRANT_DB_USER_FAILED] => Array
(
[0] => Unable to grant privileges to database users.
)

)