[15.0][FIX] hr_holidays_public: wrong computation in case resources in different countries

[gurneyalex]

Fix an issue in hr_holidays_public where
resource.calendar::_attendance_intervals_batch_exclude_public_holidays
would return a wrong result when called with multiple resources working
in different countries.

The original implementation uses a context key employee_id to find the
employee, which only allows this method to be called with a single
employee. The fix searches for the employees related to the resources
passed in arguments, and default to the context key if there are no
provided resources.

Also rework the implementation to use a python set rather than a list
for faster in test.

[pedrobaeza]

Can you add a regression test that exercises the problem you have found?

[gurneyalex]

@pedrobaeza currently the test is in a customer-specific module, at a higher level. I'll addapt it for this module soon but I need to hotfix this in prod first ;)

[pedrobaeza]

@gurneyalex please amend the PR without merge commits and add the regression test.

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖

[gurneyalex]

@pedrobaeza done :-)

[pedrobaeza]

Thanks. I still see two commits (one being fixup). Please squash them, as the bot can't do it.

[github-actions]

There hasn't been any activity on this pull request in the past 4 months, so it has been marked as stale and it will be closed automatically if no further activity occurs in the next 30 days.
If you want this PR to never become stale, please ask a PSC member to apply the "no stale" label.

[AaronHForgeFlow]

Code LG

[pedrobaeza]

@gurneyalex can you please squash your 2 commits into one? ocabot doesn't do it.

[dreispt]

Superseded by #98