Fix groups.update not appending ?asJob=True to URL when as_job=True

[Copilot]

When calling server.groups.update(group, as_job=True), the asJob query parameter was never added to the request URL, so the server returned a GroupItem response instead of a JobItem, causing an IndexError when the code tried to parse it as a job.

Changes

• groups_endpoint.py: Appends ?asJob=True to the URL when as_job=True, and raises ValueError early for local groups (which don't support async updates)
• test/test_group.py: Adds test_update_ad_async (verifies JobItem is returned) and test_update_local_async (verifies ValueError for local groups)
• test/assets/group_update_async.xml: Adds fixture with a minimal async job response

# Previously raised: IndexError: list index out of range
job = server.groups.update(ad_group, as_job=True)
assert isinstance(job, TSC.JobItem)