With thanks to @Buzzardo for finding the problem, we could change to a different metric or we could update the contributing guidelines to recommend building on HotSpot. I'm tempted to do the latter as, without an OpenJ9 CI build, it may get broken again in the future.
Comment From: Buzzardo
We should include that HotSpot is from java.net (Oracle). sdkman doesn't make that clear, and other tools may also not be helpful.
Comment From: wilkinsona
It doesn't have to be. https://adoptopenjdk.net provides both HotSpot and OpenJ9 binaries.
Comment From: snicoll
+1 for recommending to build on HotSpot.
Comment From: philwebb
When we fix this we'll also extract some of the stuff from CONTRIBUTING.adoc to the wiki
Comment From: scottfrederick
Updated in the Building from Source section of the wiki