[seL4] CI infrastructure outage

Hi Folks, Our continuous integration testing infrastructure is being relocated from CSIRO to UNSW premises this weekend. Because Sydney is in COVID lockdown, and because we're reworking the system not to rely on commercial software we no longer have a licence for (Atlassian Bamboo), we will probably not have everything working again for two or three weeks.

The upshot for you is that any pull request that needs extensive testing will not be merged for at least two weeks, possibly longer.

Peter C