Test HTMLUnit 4.21.0 in Jenkins test harness

[MarkEWaite]

Test HTMLUnit 4.21.0 in Jenkins test harness

Do not merge.

HTMLUnit 4.19.0 and 4.20.0 were unable to process some of the JavaScript used in the Jenkins test harness. Issue:

• HTMLUnit 4.19.0 and 4.20.0 report 'caller is not a function' in the Jenkins test harness HtmlUnit/htmlunit#1064

Resolved in HTMLUnit 4.21.0

Pull requests:

• Test with HTMLUnit 4.21.0 incremental jenkins-test-harness#1139
• Bump org.htmlunit:htmlunit from 4.18.0 to 4.21.0 jenkins-test-harness-htmlunit#203

Testing done

• Checked that automated tests pass for 3 sample test classes. Rely on ci.jenkins.io to test the rest

Proposed changelog entries

• N/A

Proposed changelog category

/label skip-changelog

Proposed upgrade guidelines

N/A

Submitter checklist

• The issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood (see examples). Fill in the Proposed upgrade guidelines section only if there are breaking changes or changes that may require extra steps from users during upgrade.
• There is automated testing or an explanation as to why this change has no tests.
• For dependency updates, there are links to external changelogs and, if possible, full differentials.

Desired reviewers

N/A

Before the changes are marked as ready-for-merge:

Maintainer checklist

• There are at least two (2) approvals for the pull request and no outstanding requests for change.
• Conversations in the pull request are over, or it is explicit that a reviewer is not blocking the change.
• Changelog entries in the pull request title and/or Proposed changelog entries are accurate, human-readable, and in the imperative mood.
• Proper changelog labels are set so that the changelog can be generated automatically.
• If the change needs additional upgrade steps from users, the upgrade-guide-needed label is set and there is a Proposed upgrade guidelines section in the pull request title (see example).
• If it would make sense to backport the change to LTS, be a Bug or Improvement, and either the issue or pull request must be labeled as lts-candidate to be considered.

[MarkEWaite]

Tests passed. Closing the pull request