Fix down migration for promotion_orders promotions foreign key

[rabbitbike]

Summary

The most recent migration AddPromotionOrderPromotionForeignKey has an incorrect down method.
The remove_foreign_key method has an incorrect "to_table" in the second parameter.

This migration creates a foreign key between spree_orders_promotions and spree_promotions, so the down method should refer to spree_promotions instead of spree_orders.

If you rollback this migration you will be removing the foreign key between spree_orders_promotions and spree_orders.
This causes the rollback of the previous migration to fail with a Table 'spree_orders_promotions' has no foreign key for spree_orders error, as it correctly tries to remove the same foreign key.

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c9b62b1) 88.55% compared to head (69e178f) 88.55%.
Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5642   +/-   ##
=======================================
  Coverage   88.55%   88.55%           
=======================================
  Files         685      685           
  Lines       16406    16406           
=======================================
  Hits        14528    14528           
  Misses       1878     1878           

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[kennyadsl]

Thank you! ❤️

[github-actions]

💚 All backports created successfully

Status	Branch	Result
✅	v4.3

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