fix: remove broken organisers eager load on Workshop queries

[mroderick]

Problem

PR #2682 introduced a load_events method that eagerly loads :organisers on Workshop:

Workshop.includes(:chapter, :sponsors, :host, :permissions, :organisers)

The organisers association has a scope condition on the join table:

has_many :organisers, -> { where('permissions.name' => 'organiser') }, through: :permissions, source: :members

When Rails preloads this with the separate-query strategy (which it does here because .where(id: [...]) is a simple query), it generates:

SELECT "members".* FROM "members" WHERE "permissions"."name" = 'organiser' AND "members"."id" IN (...)

This references permissions.name without joining permissions, causing PG::UndefinedTable: missing FROM-clause entry for table "permissions".

Context

PR #2679 already fixed this exact same bug for Event and Meeting by removing :organisers from their eager loads. PR #2682 reintroduced it on Workshop in the new load_events method, under the old assumption that Workshop's complex associations still forced Rails to use eager_load (LEFT JOINs). The .where(id: [...]) pattern in load_events triggers preloading instead, so the broken SQL resurfaces.

Fix

Remove :organisers from the Workshop includes in load_events.

Verification

• Tests pass
• Deployed to staging and verified /events/past loads successfully (was returning 500 before)