ci: Switch to macOS 15 Sequoia Intel-based image #1759

1. 
   hebasto commented at 7:30 pm on October 15, 2025: member

   This is an alternative to #1755.

   More details from the GHA developers:

   Apple has discontinued support for the x86_64 (Intel) architecture going forward. GitHub will no longer support this architecture on macOS after the macOS 15 runner image is retired in Fall 2027.

2. ci: Switch to macOS 15 Sequoia Intel-based image

   The `macos-13` image has been deprecated and will be unavailable soon.
   See: https://github.com/actions/runner-images/issues/13045.

   8bc50b72ff
3. hebasto force-pushed on Oct 16, 2025
4. 
   hebasto commented at 5:24 pm on October 16, 2025: member

   https://github.com/LouisBrunner/valgrind-macos/pull/147 has just been merged, so this PR has been updated and undrafted.
5. hebasto marked this as ready for review on Oct 16, 2025
6. hebasto renamed this:
   [WIP] ci: Switch to macOS 15 Sequoia Intel-based image
   ci: Switch to macOS 15 Sequoia Intel-based image
   on Oct 16, 2025
7. real-or-random approved
8. 
   real-or-random commented at 7:03 am on October 17, 2025: contributor

   ACK 8bc50b72ff600f1b3cc05003c2de35a355512aab
9. real-or-random added the label ci on Oct 17, 2025
10. real-or-random added the label tweak/refactor on Oct 17, 2025
11. real-or-random merged this on Oct 17, 2025
12. real-or-random closed this on Oct 17, 2025

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13. hebasto deleted the branch on Oct 17, 2025

Contributors
hebasto real-or-random

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ci tweak/refactor