[llvm] workflows/build-ci-container: Make sure to only test local containers (PR #120827)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

Why would it be trying to pull if the container exists locally?

The container shouldn't exist in the remote with the new tag.

Either way, seems like this fixes the issue, so approval for that.

https://github.com/llvm/llvm-project/pull/120827