[cherry-pick]Add banner message UI test case

[YangJiao0817]

Fix #19272

Thank you for contributing to Harbor!

Comprehensive Summary of your change

Issue being fixed

Fixes #(issue)

Please indicate you've done the following:

• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[codecov]

Codecov Report

Merging #19530 (12a8245) into release-2.9.0 (5cbb1b0) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@                Coverage Diff                @@
##           release-2.9.0   #19530      +/-   ##
=================================================
- Coverage          67.44%   67.42%   -0.02%     
=================================================
  Files                993      993              
  Lines             108932   108932              
  Branches            2752     2752              
=================================================
- Hits               73473    73452      -21     
- Misses             31505    31527      +22     
+ Partials            3954     3953       -1     

Flag	Coverage Δ
unittests	67.42% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 4 files with indirect coverage changes