Fix firebird tests

Author: bahusoid

src/NHibernate.Test/TestCase.cs

@@ -293,11 +293,10 @@ protected virtual void CreateSchema()
 
 		protected virtual void DropSchema()
 		{
-			using (var optionalConnection = OpenConnectionForSchemaExport())
-				DropSchema(OutputDdl, SchemaExport, Sfi, optionalConnection);
+			DropSchema(OutputDdl, SchemaExport, Sfi, OpenConnectionForSchemaExport);
 		}
 
-		public static void DropSchema(bool useStdOut, SchemaExport export, ISessionFactoryImplementor sfi, DbConnection optionalConnection = null)
+		public static void DropSchema(bool useStdOut, SchemaExport export, ISessionFactoryImplementor sfi, Func<DbConnection> getConnection = null)
 		{
 			if (sfi?.ConnectionProvider.Driver is FirebirdClientDriver fbDriver)
 			{
@@ -310,7 +309,8 @@ public static void DropSchema(bool useStdOut, SchemaExport export, ISessionFacto
 				fbDriver.ClearPool(null);
 			}
 
-			export.Drop(useStdOut, true, optionalConnection);
+			using(var optionalConnection = getConnection?.Invoke())
+				export.Drop(useStdOut, true, optionalConnection);
 		}
 
 		/// <summary>