[CI] {p0=mixed_cluster/30_ml_jobs_crud/Test get old cluster categorization job} fails

[droberts195]

Build scan:

• https://gradle-enterprise.elastic.co/s/3ozjbmlaaxyru
• https://gradle-enterprise.elastic.co/s/xssbbmd4njsbe
• https://gradle-enterprise.elastic.co/s/urkh2ymlzxk56

Repro line:

./gradlew ':x-pack:qa:rolling-upgrade:v7.11.0#bwcTest'

Reproduces locally?:

No

Applicable branches:

master

Failure history:

Started failing yesterday: https://build-stats.elastic.co/app/kibana#/discover?_g=(refreshInterval:(pause:!t,value:0),time:(from:now-7d,mode:quick,to:now))&_a=(columns:!(_source),filters:!(),index:b646ed00-7efc-11e8-bf69-63c8ef516157,interval:auto,query:(language:lucene,query:'UpgradeClusterClientYamlTestSuiteIT%20AND%20%22Test%20get%20old%20cluster%20categorization%20job%22'),sort:!(process.time-start,desc))

However, looking more closely the failures yesterday are not the same problem. The [jobs.0.node] doesn't have a true value error started today.

Failure excerpt:

java.lang.AssertionError: Failure at [mixed_cluster/30_ml_jobs_crud:77]: field [jobs.0.node] doesn't have a true value

[elasticmachine]

Pinging @elastic/ml-core (:ml)

[droberts195]

Fixed by #66015