Fix concurrency issues on TransactionScope timeout #2678

Job	Run time
SqlServer2008	8m 46s
SqlServer2008-MicrosoftDataSqlClientDriver	7m 54s
PostgreSQL	6m 22s
Firebird	11m 21s
Firebird4	11m 26s
MySQL	8m 19s
Oracle	10m 54s
SQLite	6m 12s
	1h 11m 14s

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