change our CI (org-wide) to use AdoptOpenJDK

@adriaanm I wrote down "create an Adopt OpenJDK ticket, assign it to myself, say I plan to do it in January" but now I can't remember what this meant exactly... was it to add AdoptOpenJDK to our scala/scala CI matrix, or the community build, or what? if you can't remember either I can review the team meeting video and find out