Random failing MarkOccurrenceTest.markOccurrencesAfterEditorReuse

```
java.lang.AssertionError: expected:<1> but was:<0>
at org.junit.Assert.fail(Assert.java:89)
at org.junit.Assert.failNotEquals(Assert.java:835)
at org.junit.Assert.assertEquals(Assert.java:647)
at org.junit.Assert.assertEquals(Assert.java:633)
at org.eclipse.jdt.text.tests.MarkOccurrenceTest$2.condition(MarkOccurrenceTest.java:414)
at org.eclipse.jdt.text.tests.performance.DisplayHelper.waitForCondition(DisplayHelper.java:79)
at org.eclipse.jdt.text.tests.MarkOccurrenceTest.assertOccurrences(MarkOccurrenceTest.java:421)
at org.eclipse.jdt.text.tests.MarkOccurrenceTest.markOccurrencesAfterEditorReuse(MarkOccurrenceTest.java:210)
```
https://ci.eclipse.org/jdt/job/eclipse.jdt.ui-github/job/PR-1086/3/testReport/junit/JdtTextTestSuite%20org.eclipse.jdt.text.tests/MarkOccurrenceTest/markOccurrencesAfterEditorReuse/

Start with MarkOccurrenceTest.markOccurrencesAfterEditorReuse at MarkOccurrenceTest.java:210 and its assertion at line 421, then inspect DisplayHelper.waitForCondition at DisplayHelper.java:79. Run the named test and compare failures with the linked CI test report. Done means the test reliably observes the expected occurrence after editor reuse.

Written by the indexing model from the issue text.