Try to detect a sitation where the hash of the file has changed since the referendum has started

[rzadp]

If a referendum gets created, and since that someone pushes a commit and the hash of the referendum changes, the action will not find the referendum and will not merge the PR (which is good).

However, we could try to detect this situation and inform the user that the file contents has changed and suggest to roll-back the PR to the proper commit.