fix: copy prompt skipped was missing

[TerryHowe]

What this PR does / why we need it:

This is a bit confusing, but previously, OnCopySkipped prompted with "Exists" and PostCopy prompted with "Skipped". I think this was changed accidentally.

https://github.com/oras-project/oras/blob/release-1.2/cmd/oras/root/cp.go#L180:L189

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.54%. Comparing base (d4eccf4) to head (7e29fa1).
Report is 1 commits behind head on main.

Files	Patch %	Lines
cmd/oras/internal/display/status/text.go	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1484   +/-   ##
=======================================
  Coverage   85.54%   85.54%           
=======================================
  Files         113      113           
  Lines        3936     3936           
=======================================
  Hits         3367     3367           
  Misses        342      342           
  Partials      227      227           

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[qweeah]

Nice catch, added unit test for that.

[FeynmanZhou]

The CodeCov scan seems failed in the CI. Should we fix it before merging this PR?

[TerryHowe]

Coverage on this file is 90% from my reading, but it just happens that renaming successors happens to touch a part of the code that is not tested. I think it makes sense to merge anyway here.

[TerryHowe]

I'm going to ignore the bogus coverage report.