fix: push bug when multi tagging

[qweeah]

What this PR does / why we need it:
This PR fixes a bug in oras push.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #849

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test, E2E test?
• Does this change require a documentation update?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov-commenter]

Codecov Report

Merging #850 (6ff560c) into main (8c238a9) will not change coverage.
The diff coverage is n/a.

❗ Current head 6ff560c differs from pull request most recent head 244c0f7. Consider uploading reports for the commit 244c0f7 to get more accurate results

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@@           Coverage Diff           @@
##             main     #850   +/-   ##
=======================================
  Coverage   66.89%   66.89%           
=======================================
  Files          21       21           
  Lines         879      879           
=======================================
  Hits          588      588           
  Misses        245      245           
  Partials       46       46           

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[shizhMSFT]

LGTM