fix: POS idx issue in taxes table while merging

[nemesis189]

Problem:
While merging POS invoices, the idx parameter was not being tracked so during calculation of taxes it would get overwritten

Solution:
Keeping track of idx in the merging logic itself where taxes are added

[codecov]

Codecov Report

Merging #28389 (a429820) into develop (c0f06bc) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop   #28389      +/-   ##
===========================================
- Coverage    55.24%   55.23%   -0.02%     
===========================================
  Files         1119     1119              
  Lines        66553    66572      +19     
===========================================
  Hits         36768    36768              
- Misses       29785    29804      +19     

Impacted Files	Coverage Δ
...ype/pos_invoice_merge_log/pos_invoice_merge_log.py	75.92% <100.00%> (+0.27%)	⬆️
...work_order_stock_report/work_order_stock_report.py	50.00% <0.00%> (-50.00%)	⬇️
...s/doctype/promotional_scheme/promotional_scheme.py	91.36% <0.00%> (-4.60%)	⬇️
...ctype/woocommerce_settings/woocommerce_settings.py	80.00% <0.00%> (-4.00%)	⬇️
...eport/item_variant_details/item_variant_details.py	84.33% <0.00%> (-3.62%)	⬇️
erpnext/education/doctype/student/student.py	73.68% <0.00%> (-3.16%)	⬇️
erpnext/stock/report/stock_ageing/stock_ageing.py	90.51% <0.00%> (-2.92%)	⬇️
...ion/doctype/course_enrollment/course_enrollment.py	44.00% <0.00%> (-2.00%)	⬇️
...wise_balance_history/batch_wise_balance_history.py	91.37% <0.00%> (-1.73%)	⬇️
erpnext/stock/reorder_item.py	74.35% <0.00%> (-1.71%)	⬇️
... and 25 more

[nextchamp-saqib]

@Mergifyio backport version-13-hotfix

[mergify]

backport version-13-hotfix

🟠 Waiting for conditions to match

• merged [:pushpin: backport requirement]

[mergify]

backport version-13-hotfix

✅ Backports have been created

• #28411 fix: POS idx issue in taxes table while merging (backport #28389) has been created for branch version-13-hotfix