Replace deprecated datetime.utcnow() with timezone-aware alternative

[jay-tau]

The current implementation in /lib/security/howdy/compare.py uses the deprecated datetime.datetime.utcnow() method, which triggers the following deprecation warning:

/lib/security/howdy/compare.py:57: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
  "Date: " + datetime.datetime.utcnow().strftime("%Y/%m/%d %H:%M:%S UTC"),

This method is scheduled for removal in a future Python version. We need to update our code to use the recommended timezone-aware alternative.

Benefits

• Eliminates the deprecation warning
• Ensures compatibility with future Python versions
• Uses the recommended timezone-aware approach for handling UTC datetimes

Additional notes

• This change may require updating the minimum Python version requirement for the project
• We should consider scanning the codebase for other instances of datetime.utcnow() and update them as well.

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Linux distribution (if applicable): EndeavourOS

Howdy version (sudo howdy version): Howdy 2.6.1