BUGFIX: Close connection to reset transaction

[mhsdesign]

When the database is empty, the doctrine migrations will be run via executeMigrations.
Though that leads to a transaction still being active:

array(2) {
  ["getTransactionNestingLevel"]=>
  int(119)
  ["isTransactionActive"]=>
  bool(true)
}

To work around this we close the connection, leading to the excepted state of no transaction. (The same state if the schema would already exist)

array(2) {
  ["getTransactionNestingLevel"]=>
  int(0)
  ["isTransactionActive"]=>
  bool(false)
}

This change is required for neos/neos-development-collection#5284 so we can remove the hacky ./../flow doctrine:migrate scripts in the CI.