fix: "update cost" should ignore overridden routing times

[ankush]

steps to reproduce:

1. Create a routing
2. Create a BOM add the routing
3. Modifying the operations time and save. Operating cost will be correct.
4. Do "Update cost" it will override the operations time and overall cost will also change.

Expected: operation time should not change when "update cost" is done.

[codecov]

Codecov Report

Merging #29154 (41a1ab8) into develop (962dd5e) will increase coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop   #29154      +/-   ##
===========================================
+ Coverage    57.74%   57.76%   +0.02%     
===========================================
  Files         1110     1110              
  Lines        67991    67987       -4     
===========================================
+ Hits         39262    39275      +13     
+ Misses       28729    28712      -17     

Impacted Files	Coverage Δ
erpnext/manufacturing/doctype/bom/bom.py	86.76% <ø> (-0.09%)	⬇️
...unts/report/purchase_register/purchase_register.py	32.19% <0.00%> (-39.05%)	⬇️
...ext/accounts/report/balance_sheet/balance_sheet.py	36.36% <0.00%> (-21.82%)	⬇️
...e_purchase_register/item_wise_purchase_register.py	58.00% <0.00%> (-17.00%)	⬇️
...it_and_loss_statement/profit_and_loss_statement.py	71.42% <0.00%> (-3.90%)	⬇️
erpnext/portal/utils.py	28.98% <0.00%> (-1.45%)	⬇️
...cial_statement/consolidated_financial_statement.py	88.81% <0.00%> (-0.96%)	⬇️
erpnext/stock/reorder_item.py	76.06% <0.00%> (-0.86%)	⬇️
...em_wise_sales_register/item_wise_sales_register.py	51.36% <0.00%> (-0.46%)	⬇️
.../report/accounts_receivable/accounts_receivable.py	71.36% <0.00%> (-0.43%)	⬇️
... and 24 more