docs: add two more amend commits to simulate temporary amend commits sharing.rst made reference to temporary amend commits and used them to demonstrate that hidden commits are not exchanged. Nowadays, evolve doesn't create such commits, but it still makes sense to show how they are handled during the exchange process. So let's add two more amend commits, one for each repo. This way the guide doesn't have to be updated too much, but doesn't lose this important detail of working with evolve. Unfortunately, this means that tons of hashes change, but it's better than to have figure 4 demonstrate absolutely nothing. Temporary amend commits were removed from test-sharing.t in 06844693bb21, but sharing.rst continued using them for demonstration purposes. It might've been better to replace at least some of the temporary amend commits by extra amends back then, but oh well.