fix: Sales Order cancellation message

[GangaManoj]

Problem:

When cancelling a Sales Order which has a Sales Invoice in the draft state linked to it:

• The user is directed to 'cancel' the linked invoice, even though only submitted invoices can be cancelled.
• If the invoice has more than one Item, the name of the invoice will be repeated multiple times(as many times as there are Items in it).

Fix:

• Edit the message to instruct the user to delete the linked invoice instead.
• Only display the name of the invoice once, irrespective of the number of Items in it.

Additional changes:

• Remove redundant code
• Add tests

[codecov]

Codecov Report

Merging #27735 (cc07c71) into develop (f24ed67) will increase coverage by 0.09%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop   #27735      +/-   ##
===========================================
+ Coverage    55.10%   55.20%   +0.09%     
===========================================
  Files         1255     1255              
  Lines        67929    67913      -16     
===========================================
+ Hits         37431    37488      +57     
+ Misses       30498    30425      -73     

Impacted Files	Coverage Δ
erpnext/selling/doctype/sales_order/sales_order.py	77.58% <100.00%> (+1.19%)	⬆️
erpnext/education/doctype/student/student.py	73.95% <0.00%> (-3.13%)	⬇️
...value/warehouse_wise_item_balance_age_and_value.py	92.59% <0.00%> (-2.47%)	⬇️
erpnext/stock/stock_ledger.py	85.32% <0.00%> (-2.00%)	⬇️
...ion/doctype/course_enrollment/course_enrollment.py	45.09% <0.00%> (-1.97%)	⬇️
erpnext/portal/utils.py	30.00% <0.00%> (-1.43%)	⬇️
erpnext/stock/reorder_item.py	76.27% <0.00%> (-0.85%)	⬇️
...ype/account/chart_of_accounts/chart_of_accounts.py	77.55% <0.00%> (-0.69%)	⬇️
...next/accounts/doctype/subscription/subscription.py	82.02% <0.00%> (-0.57%)	⬇️
erpnext/stock/get_item_details.py	79.51% <0.00%> (-0.46%)	⬇️
... and 19 more

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed within a week if no further activity occurs, but it only takes a comment to keep a contribution alive :) Also, even if it is closed, you can always reopen the PR when you're ready. Thank you for contributing.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed within a week if no further activity occurs, but it only takes a comment to keep a contribution alive :) Also, even if it is closed, you can always reopen the PR when you're ready. Thank you for contributing.