Fix fmu_copy_revision prints wrong disk space above 1024 g

[HakonSohoel]

_filesize() divided size by 1024 one extra time when it reached
the largest supported unit ("G"), reporting revisions >= 1024 G in the
wrong magnitude (e.g. 2.0 T showed as 2.0 G)

[codecov-commenter]

Codecov Report

❌ Patch coverage is 86.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.28%. Comparing base (2579f6d) to head (dd68a53).

Files with missing lines	Patch %	Lines
...c/subscript/fmu_copy_revision/fmu_copy_revision.py	86.66%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #886   +/-   ##
=======================================
  Coverage   84.28%   84.28%           
=======================================
  Files          49       49           
  Lines        7530     7530           
=======================================
  Hits         6347     6347           
  Misses       1183     1183           

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[alifbe]

LGTM 👍