[REF] Add test for existing Participant batch update cancel and fix to not call BaseI...

[REF] Add test for existing Participant batch update cancel and fix to not call BaseIPN->cancelled

I dug into what is 'achieved' by calling BaseIPN->cancelled here and everything except the bit where the contribution
is updated to cancelled is actually bypassed so a simple api call suffices.

I also discovered the cancellation of the contribution is highly conditional and arguably illogical. I will separately
log a gitlab to discuss whether it still makes sense, but I wouldn't want that discussion to derail this
no-change cleanup