Use timezone-aware datetime for SSH key cutoff date comparison

[Copilot]

Addresses feedback from #12536 to use timezone-aware datetime objects in the SSH key write access deprecation check.

Changes

• Updated datetime comparison to use UTC timezone (datetime.timezone.utc) from Python's standard library
• No external dependencies required (removed pytz in favor of standard library)

Before:

hard_failure = datetime.datetime.now() >= datetime.datetime(2025, 12, 1)

After:

now = datetime.datetime.now(tz=datetime.timezone.utc)
hard_failure = now >= datetime.datetime(2025, 12, 1, 0, 0, 0, tzinfo=datetime.timezone.utc)

This prevents inconsistent behavior across different server timezones and uses UTC (UTC+0) as the standard timezone for server-side operations.

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[stsewd]

@copilot what about making it utc-0 instead?

[Copilot]

@copilot what about making it utc-0 instead?

Changed to use UTC (datetime.timezone.utc) instead of Pacific Time. This also removes the pytz dependency in favor of the standard library. Changes made in commit d187a8d.

[stsewd]

Good bot