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

[Tom Stellard via llvm-commits]

tstellar wrote:

> 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.

You are correct that the `--pull=never` option is not strictly required, I just added it to be extra safe.  Removing the testing for the `:latest` tag which was only available remotely is the part of the change the fixed my problem.

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