CI : Run on Ubuntu 24.04

[johnhaddon]

Support for 20.04 is being removed from GitHub. We have the choice of 22.04 or 24.04, and updating to the latest gives us the longest period before we have to do this again.

[murraystevenson]

The changes look good to me, though as mentioned offline it does introduce what appears to be a benign ERROR: ld.so: object 'libSegFault.so' from LD_PRELOAD cannot be preloaded (cannot open shared object file): ignored. error at the beginning of most steps due to our adding LD_PRELOAD=libSegFault.so to GITHUB_ENV in "Install toolchain (Linux)".

It seems this error is coming from the base Ubuntu OS and not our build container as libSegFault.so isn't installed by default in 22.04 or 24.04, likely because in 22.04 it moved to be being provided by glibc-tools.

Putting LD_PRELOAD: libSegFault.so under env: results in the same error, so we may have to resort to setting this within the run: block of any step that requires it...