ci: Convert arm64 Cirrus tasks to GHA jobs #1689

1. 
   hebasto commented at 7:56 pm on June 19, 2025: member

   This PR:

   1. Consolidates all CI jobs.

   2. Frees up resources allocated to Cirrus permanent workers.

2. ci: Rename Docker image tag to reflect architecture b77aae9226
3. ci: Add `arm64` architecture to `docker_cache` job bcf77346b9
4. ci: Switch `arm64_debian` from QEMU to native `arm64` Docker image e814b79a8b
5. ci: Move `gcc-snapshot` build for `arm64` from Cirrus to GHA 5fafdfc30f
6. ci: Move Valgrind build for `arm64` from Cirrus to GHA 004f57fcd8
7. real-or-random added the label ci on Jun 20, 2025
8. real-or-random approved
9. 
   real-or-random commented at 9:26 am on June 24, 2025: contributor

   ACK 004f57fcd86de3ea8cb0e6a16f5bb665db9d1ed4
10. real-or-random added the label refactor/smell on Jun 24, 2025
11. 
    real-or-random commented at 9:34 am on June 24, 2025: contributor

    Hm, this adds another ~1.6 GB to the cache, which has a 10 GB limit. I think it’s fine, but we need to check if we run into cache trashing, e.g., if we have PRs changing the Dockerfile. @hebasto What do you think?

Contributors
hebasto real-or-random

Labels
ci refactor/smell