fix: Currency fix for cost field in subscription plan

[nemesis189]

Issue:
The cost field of Subscription plan would always have the company currency

Before:

After:

Fix:
Picking up the currency from the currency link field in the form

steps:

1. create a new Subscription Plan with currency different than the company currency
2. Save and check in the list view if correct one is displayed

[codecov]

Codecov Report

Merging #28821 (438e6a3) into develop (9a644f6) will increase coverage by 8.46%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop   #28821      +/-   ##
===========================================
+ Coverage    46.80%   55.27%   +8.46%     
===========================================
  Files         1122     1122              
  Lines        66777    66828      +51     
===========================================
+ Hits         31255    36936    +5681     
+ Misses       35522    29892    -5630     

Impacted Files	Coverage Δ
...nts/doctype/accounts_settings/accounts_settings.py	97.50% <0.00%> (-2.50%)	⬇️
.../hr/doctype/upload_attendance/upload_attendance.py	44.69% <0.00%> (-1.52%)	⬇️
...next/accounts/doctype/subscription/subscription.py	81.74% <0.00%> (-0.57%)	⬇️
erpnext/hooks.py	0.00% <0.00%> (ø)
erpnext/regional/saudi_arabia/setup.py	0.00% <0.00%> (ø)
...ext/payroll/doctype/payroll_entry/payroll_entry.py	71.02% <0.00%> (+0.23%)	⬆️
...stock/doctype/purchase_receipt/purchase_receipt.py	90.37% <0.00%> (+0.34%)	⬆️
erpnext/accounts/doctype/account/account.py	71.76% <0.00%> (+0.39%)	⬆️
erpnext/hr/utils.py	74.29% <0.00%> (+0.40%)	⬆️
erpnext/selling/doctype/sales_order/sales_order.py	77.58% <0.00%> (+0.42%)	⬆️
... and 185 more