[llvm] [libc] Switch libc-shared-tests precommit CI to use docker image. (PR #197962)

[Jeff Bailey via llvm-commits]

================
@@ -48,6 +48,8 @@ jobs:
   linux-cross-arch-shared:
     name: libc-shared-tests on (${{ matrix.arch }})
     runs-on: ubuntu-24.04
+    container:
+      image: 'ghcr.io/llvm/libc-ubuntu-24.04:70cbd7591abe'
----------------
kaladron wrote:

This a tag, not a git sha1, so this is the entire thing.

https://github.com/llvm/llvm-project/pull/197962