Fix the "Select text with the pointer hovering an existing highlight must check that an existing highlight is ignored on hovering" integration test

[timvandermeij]

This integration test fails consistently on only the Windows bot with the following traceback (see http://54.193.163.58:8877/662f7dec318944a/output.txt):

Failures:
1) Highlight Editor Select text with the pointer hovering an existing highlight must check that an existing highlight is ignored on hovering
  Message:
�[31m    In chrome: Expected 1 to equal 0.�[0m
  Stack:
        at <Jasmine>
        at file:///C:/pdfjs/botio-files-pdfjs/private/662f7dec318944a/test/integration/highlight_editor_spec.mjs:1880:58
        at async Promise.all (index 1)
        at async UserContext.<anonymous> (file:///C:/pdfjs/botio-files-pdfjs/private/662f7dec318944a/test/integration/highlight_editor_spec.mjs:1834:7)

The earliest occurrence I could find of this test failure is #18698 (comment), so perhaps that patch introduced a regression (other than #18716). We could try to check if it still fails without that patch, and if so we might have a better idea about what changed.

PR #18721 attempts to debug/resolve this issue.