backpopulate_xpro_data is not picking up new programs or program course runs

[mbertrand]

Steps to Reproduce

Run backpopulate_xpro_data

Expected Behavior

New programs and program course runs are added for xpro.

Actual Behavior

New programs and program course runs are not added, but the command completes successfully.

[mbertrand]

This actually seems to have been caused by confusion over the displayed start dates in search results (for courses/runs), that previously often defaulted to enrollment start date, which for xpro is often far earlier than the actual start date. Should be fixed by #3850. For all programs currently returned by the API, the start date is way back in 2019 or 2020.