fix: Payment Terms Status for Sales Order report show all payment terms from orders (not only when there is a payment terms template)

[FHenry]

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The report Payment Terms Status for Sales Order display payment schedule only for orders with Payment Terms template
It should display all payment terms schedule for order even if the is no template but also manually entered payments terms

Explain the details for making this change. What existing problem does the pull request solve?

Actually the filter
(so.payment_terms_template != "NULL")
is not correct, at least it have to be
(so.payment_terms_template.notnull())
If you really want this filter

Actually will compare NULL as a string :
tabSales Order.payment_terms_template <> "NULL"
as it should be :
NOT tabSales Order.payment_terms_template IS NULL

But any way, there is no need to filter incoming amount from orders with payment terms template, just payment term is enough. The payment Terms template is not use else where in the report

no-doc
no-test

Note to reviewer, if this PR is accepted, could you please add github label backport to version-15 and version-14 ?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (64cb115) 60.15% compared to head (735576a) 60.15%.
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #39331   +/-   ##
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  Coverage    60.15%   60.15%           
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  Files          757      757           
  Lines        70696    70696           
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+ Hits         42525    42526    +1     
+ Misses       28171    28170    -1     

Files	Coverage Δ
...ales_order/payment_terms_status_for_sales_order.py	80.99% <ø> (ø)

... and 1 file with indirect coverage changes