3c8f5e48f7 ci: Treat SHA1 LLVM signing key as warning (will)
Pull request description:
The current SHA1 LLVM signing key is considered not secure since
2026-02-01T00:00:00Z which makes this run fail when downloading
packages.
See: https://github.com/llvm/llvm-project/issues/153385
Apply the fix from the issue to temporarily to treat this error as a
warning, until the upstream key can be updated.
This PR should be reverted once the upstream key is updated.
ACKs for top commit:
hebasto:
ACK 3c8f5e48f7, tested by running the "iwyu" CI job locally on Ubuntu 25.10 after burning all podman's caches.
Tree-SHA512: fbccf98bfd73cb338670f1ceea994d277d746acbc88b9b90a403d9a59d82abda0f3ba34c4d484b70926340c2d0c873259f930c36ccd4f9d18bb1d22d49ee70c4