[MISC] Show start/end time in UTC time in list-backups output

[lucasgameiroborges]

Issue

Output of command was converting timezones to local time, which can generate confusion + unit test was failing if local timezone not UTC.

Thanks to @dragomirp for raising this issue.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.89%. Comparing base (2c0f64b) to head (fa0d96e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #551   +/-   ##
=======================================
  Coverage   70.89%   70.89%           
=======================================
  Files          11       11           
  Lines        3024     3024           
  Branches      535      535           
=======================================
  Hits         2144     2144           
  Misses        764      764           
  Partials      116      116           

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[marceloneppel]

Thanks!