Custom population degree programmes do not match

[tttriple]

fix first #4723

then groom...

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login as: tttriple

choose custom population: KP_laakis_2023-2024

notice the difference in degree programme student counts between list and filter

[valtterikantanen]

The reason for this behavior is that the filter takes all study rights into account (i.e. it's possible for a student to be included in multiple groups under the filter). Meanwhile, the table only shows the latest programme for each student (this is stated in the info box).