fix(celery): populate origin and hostname as distinct span attributes

[ahmed5145]

Description

Celery's set_attributes_from_context aliased origin to hostname, so on
prefork workers the worker-thread origin (e.g. gen8@host) overwrote the real
worker hostname (e.g. celery@host) in the celery.hostname span attribute.
Metrics already used the correct hostname (task.request.hostname), so spans
and metrics disagreed. This drops the alias so celery.origin and
celery.hostname are emitted as distinct span attributes, matching the actual
Celery request fields.

Fixes #3096

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• tox -r -e py314-test-instrumentation-celery (30 passed) on Windows /
  Python 3.14 against core commit d9f34e7.
• Extended test_set_attributes_from_context to assert that a context
  containing both origin and hostname sets celery.origin and
  celery.hostname to their own values independently.

Does This PR Require a Core Repo Change?

• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added (extended test_set_attributes_from_context)
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: ahmed5145 / name: Ahmed Mohamed (fd511b8)