Bumping tool_coverage-linux to 24G of memory to avoid OOM kills (#50700)

OK, I'm just going to double the original 12G to 24G and see if that's enough. It has been making more progress with more memory, so it's not an infinite loop (probably), but still is getting OOM killed.

Something has clearly changed, but looking at the commits, I can't see it: the OOM kills started on a PR that was an error message change.

TBR= @Hixie