Clone job inputs in the Build model

The following discussion from !194719 (merged) should be addressed:

• @avielle started a discussion: (+11 comments)

  @lauraXD @furkanayhan one of these Ci::Processable#clone specs was failing, and I was able to make it pass just by modifying some pieces of the test setup. That feels wrong 🤔 Do either of you know where/why we use the clone method and what we "should" do here?