chore: update err-msg with notation

[junczhu]

Description

What this PR does / why we need it:

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

Fixes error msg in notation verifier.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• CI

Checklist:

• Does the affected code have corresponding tests?
• Are the changes documented, not just with inline documentation, but also with conceptual documentation such as an overview of a new feature, or task-based documentation like a tutorial? Consider if this change should be announced on your project blog.
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have appropriate license header?

Post Merge Requirements

• MAINTAINERS: manually trigger the "Publish Package" workflow after merging any PR that indicates Helm Chart Change

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pkg/verifier/notation/notation.go	50.00%	1 Missing ⚠️

Files with missing lines	Coverage Δ
pkg/verifier/notation/notation.go	98.07% <50.00%> (+9.95%)	⬆️

... and 18 files with indirect coverage changes

[junczhu]

We have a corner case that cannot be covered by test on line 261

The check is necessary by following Marshall best practice, and I will have the coverage improved after recover mentioned in issue #1752

In conclusion we can skip the coverage test for this PR.

cc\ @binbin-li