update uptime reading for OMV 6.x

[Yannik25]

In OMV 6.x update is shown as:
'uptime': 873077.17
instead of previously in OMV 5.x as:
'uptime': '14 days 0 hours 14 minutes 49 seconds'

Proposed change

Type of change

• Bugfix
• New feature
• Code quality improvements to existing code or addition of tests
• Documentation

Additional information

Checklist

• The code change is tested and works locally.
• The code has been formatted using Black.
• Tests have been added to verify that the new code works.
• Documentation added/updated if required.