[ci] Investigate & update Ubuntu version for persistent CI instances

[tyler-yankee]

We have the following CI instances that stay up 24/7:

• drake-license → bionic
• drake-jenkins → noble
• drake-certificates → jammy
• drake-webdav → noble
• drake-cdash → jammy

We only have up-to-date documentation for what Ubuntu version these are currently running for some of them, and it's scattered over a few different places. In #22996 (and other follow-up issues, see the original for the paper trail), we switched over the development platform to Noble. While updating these CI machines isn't strictly required to accompany these changes, it's something we should take care of while we're all thinking about it.