ci: Clean the cache regularly to test on new compiler snapshots #1691

1. 
   real-or-random commented at 7:02 am on June 20, 2025: contributor

   We can use a GHA cron job to delete the cache every few weeks automatically.

   Originally posted by @real-or-random in #1690 (comment)

2. real-or-random added the label ci on Jun 20, 2025

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