dev: Make sure database is initialized on the CI

There was a "critical" error when running tests against the PGSQL
database:

> [critical] Error thrown while running command "dbal:run-sql
> --connection=default 'SELECT pid, pg_terminate_backend(pid) FROM
> pg_stat_activity WHERE datname = current_database() AND pid <>
> pg_backend_pid()'". Message: "An exception occurred in the driver:
> SQLSTATE[08006] [7] connection to server at "127.0.0.1", port 5432
> failed: FATAL:  database "bileto_test" does not exist"

In fact, this error didn't prevent the tests to be run, but it bothered
me.

.github/workflows/tests.yml

@@ -30,6 +30,7 @@ jobs:
                 env:
                     POSTGRES_USER: postgres
                     POSTGRES_PASSWORD: postgres
+                    POSTGRES_DB: bileto_test
                 ports:
                     - 5432:5432
                 options: >-
@@ -81,6 +82,7 @@ jobs:
                     - 3306:3306
                 env:
                     MARIADB_ROOT_PASSWORD: mariadb
+                    MARIADB_DATABASE: bileto_test
                 options: >-
                     --health-cmd="mysqladmin ping"
                     --health-interval=10s