refactor: if() to CASE WHEN

[c-p-b]

instead of using MariaDB IF() function, we change this to be CASE WHEN, which is also supported syntax by Postgres.

[codecov]

Codecov Report

Merging #31360 (159e5d0) into develop (10583eb) will decrease coverage by 0.11%.
The diff coverage is 97.14%.

@@             Coverage Diff             @@
##           develop   #31360      +/-   ##
===========================================
- Coverage    63.64%   63.53%   -0.12%     
===========================================
  Files          984      984              
  Lines        67562    67573      +11     
===========================================
- Hits         43001    42933      -68     
- Misses       24561    24640      +79     

Impacted Files	Coverage Δ
...xt/accounts/doctype/journal_entry/journal_entry.py	68.95% <ø> (ø)
erpnext/accounts/utils.py	70.32% <ø> (ø)
.../report/procurement_tracker/procurement_tracker.py	90.19% <ø> (ø)
erpnext/controllers/accounts_controller.py	85.57% <ø> (-0.24%)	⬇️
.../hr/doctype/leave_application/leave_application.py	82.37% <ø> (ø)
erpnext/hr/utils.py	76.40% <ø> (ø)
...cturing/doctype/production_plan/production_plan.py	74.86% <ø> (ø)
...ext/manufacturing/doctype/work_order/work_order.py	78.16% <ø> (-0.15%)	⬇️
...ext/payroll/doctype/payroll_entry/payroll_entry.py	77.49% <ø> (ø)
erpnext/payroll/doctype/salary_slip/salary_slip.py	87.14% <ø> (+0.24%)	⬆️
... and 60 more