Update Ubuntu version for Ur/Web (#9463)
* Baseline Ur/Web configuration now works building the Ur/Web compiler and runtime from source
* Update Ur/Web MySQL baseline
* Get current version of Ur/Web cached queries unbroken (and tag myself as maintainer)
* For Ur/Web caching tests, switch to building Ur/Web from source
* Update Ubuntu version for Ur/Web
* Change Ur/Web's Ubuntu version to latest LTS