Fix #1112 - throw an exception if DATABASE_URL is set (#9)

* fix #1112 - throw an exception when DATABASE_URL is defined, minor test changes

* Fix code style (php-cs-fixer)

* fix typo

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Co-authored-by: PHP CS Fixer <phpcsfixer@example.com>

tests/QueueTest.php

@@ -159,6 +159,7 @@ test('tenancy is initialized when retrying jobs', function (bool $shouldEndTenan
     });
 })->with([true, false]);
 
+// todo0 this test appears to be affected by race conditions/similar
 test('the tenant used by the job doesnt change when the current tenant changes', function () {
     withTenantDatabases();