Do Ensnaring Bridge and Tortoise Formation work together?
No, Tortoise Formation has no interaction with Ensnaring Bridge.

Shroud only prevents a creature from being the target of a spell or ability. That is the only thing shroud does. Only spells or abilities that specifically use the word "target" have targets (with a few pseudo-exceptions, chiefly Auras and Equip abilities, for which the word "target" occurs in the official rules but is not usually printed on the card). If a spell or ability does not use the word "target", then shroud has no effect.

Ensnaring Bridge's ability does not use the word "target", so playing Tortoise Formation will not allow your creatures to get around the Bridge's restriction.