ReindexIT#testUpdateByQuery can fail with assertion error.

[jtibshirani]

This failure first popped up a couple times in the master intake builds, once in testDeleteByQuery and once in testUpdateByQuery. In both failures, it seems that there is an unexpected task still running after the main test logic has completed.

First build scan: https://gradle-enterprise.elastic.co/s/rasy6lapqbogy
Second build scan: https://gradle-enterprise.elastic.co/s/t5l5j3kplm2fa

A code snippet containing one of the failing assertions:

// any rethrottling after the delete-by-query is done performed with the same taskId should result in a failure
response = execute(new RethrottleRequest(taskIdToRethrottle, requestsPerSecond),
    highLevelClient()::deleteByQueryRethrottle, highLevelClient()::deleteByQueryRethrottleAsync);
assertTrue(response.getTasks().isEmpty());

[elasticmachine]

Pinging @elastic/es-distributed

[henningandersen]

Given this is only in master intake, I think this was affected by the IO problem described in #46091. Still, the 2s timeout is too aggressive, so will leave open until PR is merged.