Fix MiqTask.with_status_in scope chaining and scope leakage

[ohhAndy]

Fixes ManageIQ/manageiq-ui-classic#9471

Introduced in #16365

Problem

Calling with_status_in on an existing relation chain silently drops all preceding WHERE clauses because the scope block returns a new relation rooted at MiqTask.all instead of merging with self:

# Prior condition (`zone = 'East'`) was completely discarded:
MiqTask.with_zone("East").with_status_in("completed_ok").to_sql
# => WHERE "miq_tasks"."state" = 'Finished' AND "miq_tasks"."status" = 'Ok'

Fix

• Wrap the OR reduction in merge(...) so conditions are ANDed into the existing relation chain.
• Use MiqTask.unscoped.send(...) for each branch to prevent outer/default scopes from leaking into individual OR clauses.
• Add specs in spec/models/miq_task_spec.rb for single and multiple status chaining.

@miq-bot assign @jrafanie
@miq-bot add-label bug
@miq-bot add-reviewer @jrafanie

[miq-bot]

Checked commit ohhAndy@c191d49 with ruby 3.3.12, rubocop 1.91.0, haml-lint 0.78.0, and yamllint 1.37.1
2 files checked, 0 offenses detected
Everything looks fine. 👍