[Tech]: Fix magic numbers in `farming` tests

[bragov4ik]

Problem statement

Tests in farming pallet include magic numbers without explanation of how to obtain it. It makes it very challenging to update/fix the tests properly. This should be fixed.

One way is to check the tested logic and write down computation formulae in the comments explaining how the numbers were obtained. Another way is to calculate the results in the tests themselves using these formulae to get the expected values.

Description

No response

Definition of Done

• [ ] Tests do not have arbitrary unexplained numbers

Requirements

No response