[8.x] Fix pivot and morphpivot fresh and refresh methods

[axlon]

This PR fixes Pivot::fresh(), Pivot::refresh(), MorphPivot::fresh() and MorphPivot::refresh() which are broken after #34974 which reverted #34836.

I have tested this locally already, but I can add additional tests if these changes are okay.

[driesvints]

Can you add a test for this? Also: doesn't this re-introduces #34954?

/cc @adamthehutt

[axlon]

If I understood his comments correctly he extended Model::setKeysForSaveQuery() which was being called by Model::fresh() and Model::refresh() after my first PR.

His PR then changed this to the newly introduced Model::setKeysForSelectQuery() so that his project wouldn't break anymore (because his extended function is no longer called when it shouldn't be), which would have been fine, but the PR did not account for Pivot::fresh(), Pivot::refresh(), MorphPivot::fresh() and MorphPivot::refresh().

All this PR aims to do is fix the pivot methods which were broken by aforementioned PR, not revert his PR altogether so it shouldn't re-introduce the original issue (unless I misunderstood the change that was made)

@driesvints I will add tests in a few hours when I have some free time 👍

[axlon]

@driesvints I added tests

[adamthehutt]

Sorry about that, @axlon.

@driesvints It looks like this should be fine as far as I can tell.