fix: fix error message when output is used before format for oras discover

[wangxiaoxuan273]

What this PR does / why we need it:

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 #1348

Please check the following list:

• [x] 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?
• [x] Do all new files have an appropriate license header?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 84.64%. Comparing base (2edebad) to head (dd18fa0).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1354 +/- ## ========================================== - Coverage 84.65% 84.64% -0.01% ========================================== Files 104 104 Lines 3688 3687 -1 ========================================== - Hits 3122 3121 -1 Misses 338 338 Partials 228 228 ```

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