Add CI job that ensures every translation builds

Currently, I have to add each language individually to the branch protection rules for `main`. This a problem since we can merge PRs which fail later when building the translations for publishing.

I think we can handle this by adding a new CI job which waits on every translation and only succeeds when they all succeed.

_Originally posted by @mgeisler in https://github.com/google/comprehensive-rust/issues/2531#issuecomment-2571282773_