Ignore plantuml images for test sites

[yucheng11122017]

What is the purpose of this pull request?

• [ ] Documentation update
• [X] Bug fix
• [ ] Feature addition or enhancement
• [ ] Code maintenance
• [ ] DevOps
• [ ] Improve developer experience
• [ ] Others, please explain: Resolves #2498 Also does #2497

Overview of changes: Enable ignoring of plantuml images for test sites

Anything you'd like to highlight/discuss: nil

Testing instructions: nil

Proposed commit message: (wrap lines at 72 characters) Enable ignoring of plantuml images for test sites

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Checklist: :ballot_box_with_check:

• [ ] Updated the documentation for feature additions and enhancements
• [ ] Added tests for bug fixes or features
• [X] Linked all related issues
• [X] No unrelated changes

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Reviewer checklist:

Indicate the SEMVER impact of the PR:

• [ ] Major (when you make incompatible API changes)
• [ ] Minor (when you add functionality in a backward compatible manner)
• [x] Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

• To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

• what was the old feature that was made obsolete
• any replacement feature (if any), and
• how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

[codecov[bot]]

Codecov Report

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

Project coverage is 51.14%. Comparing base (6cc2461) to head (c6bf4b3).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2502 +/- ## ======================================= Coverage 51.14% 51.14% ======================================= Files 124 124 Lines 5359 5359 Branches 1152 1152 ======================================= Hits 2741 2741 Misses 2328 2328 Partials 290 290 ```

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[github-actions[bot]]

@kaixin-hc Each PR must have a SEMVER impact label, please remember to label the PR properly.