[llvm] [CI][Github] Hash-pin AArch64 CI image (PR #221475)

[via llvm-commits]

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@@ -41,7 +41,7 @@
       # job.  The depot containers are running on VMs, so we can use a
       # container.  This helps ensure the build environment is as close
       # as possible on both the depot runners and the llvm-premerge runners.
-      image: ${{ (startsWith(matrix.runs-on, 'depot-ubuntu-24.04-arm') && format('ghcr.io/{0}/arm64v8/ci-ubuntu-24.04',github.repository_owner) ) || null }}
+      image: ${{ (startsWith(matrix.runs-on, 'depot-ubuntu-24.04-arm') && format('ghcr.io/{0}/arm64v8/ci-ubuntu-24.04:24942433bc8a',github.repository_owner) ) || null }}
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github-advanced-security[bot] wrote:

## zizmor / 

unpinned image references: container image may be unpinned

[Show more details](https://github.com/llvm/llvm-project/security/code-scanning/2351)

https://github.com/llvm/llvm-project/pull/221475