Investigate discovery time

[mattgodbolt]

Compiler Discovery time jumped up from ~5m to 20+ minutes (sometimes 40m)

See: https://github.com/compiler-explorer/infra/actions/workflows/compiler-discovery.yml

note the build 2 months ago, November 27th, took 3m. then one on Nov 28th took 17m and was canceled, then a couple after that completed in 5m and 3m.

Then from Dec 2nd 2024 onward they've all been 20m + except one run on Dec 4th which was 3m. There was a 42m run on Jan 6th.

Something funky going on with caching?

[partouf]

compiler-explorer/compiler-explorer#7192

[mattgodbolt]

Thanks!