[18.0][FIX] rma_purchase: fix missing arguments in call to super

[StefanRijnhart]

Issue

On purchase orders with a non-default currency, currency conversion is wrong on new purchase order lines.

How to reproduce

Create a purchase order and set the currency to a non-default currency. Be sure to save the purchase order. Then click Add Product. You can see that the currency on the new line is already wrong, and is not taken from the line's purchase order.

Actual result

When a price is derived from a product supplierinfo (which has a specific currency) the rate conversion is not applied as expected.

Since 14.0! 9de5abc

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.40%. Comparing base (98d5855) to head (be7a461).
⚠️ Report is 1 commits behind head on 18.0.

Additional details and impacted files

@@           Coverage Diff           @@
##             18.0     #692   +/-   ##
=======================================
  Coverage   79.40%   79.40%           
=======================================
  Files         130      130           
  Lines        5560     5560           
  Branches      702      702           
=======================================
  Hits         4415     4415           
  Misses        920      920           
  Partials      225      225           

Files with missing lines	Coverage Δ
rma_purchase/models/purchase_order.py	57.14% <100.00%> (ø)

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