VecMem Update, main branch (2024.05.30.)

Updated Athena to use vecmem-v1.5.0.

We need this latest version to progress with testing traccc in Athena (cc @nribaric). Since AthenaExternals currently comes with vecmem-v1.1.0, I've been running into the same build issue that @pagessin and @boudreau know much too well. (Them with the Acts and GeoModel nightlies respetively.) 😦

Note that I don't believe that a full-build would be needed here. But let's see... 😉