remote-helper: inform the user of an empty patch — heartwood

The previous message is included in the error:

 ! [remote rejected] master -> refs/patches (patch commits are already included in the base branch)

To make it clearer to the user, also print a warning to tell them that the commit was in the base branch – including the commit SHA:

warn: attempted to create a patch using the commit f2de534b5e81d7c6e2dcaf58c3dd91573c0a0354, but this commit is already included in the base branch

 ``` (stderr) (fail)
 $ git push rad master:refs/patches
 warn: attempted to create a patch using the commit f2de534b5e81d7c6e2dcaf58c3dd91573c0a0354, but this commit is already included in the base branch
 To rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi
  ! [remote rejected] master -> refs/patches (patch commits are already included in the base branch)
 error: failed to push some refs to 'rad://z42hL2jL4XNk6K8oHQaSWfMgCL7ji/z6MknSLrJoTcukLrE435hVNQT4JUhbvWLX4kUzqkEStBU8Vi'

 use radicle_cli as cli;
 use radicle_cli::terminal as term;
 use crate::{hint, read_line, Options, Verbosity};
 use crate::{hint, read_line, warn, Options, Verbosity};
 #[derive(Debug, Error)]
 pub enum Error {

     let base = patch_base(head, &opts, stored)?;
     if base == *head {
         warn(format!(
             "attempted to create a patch using the commit {head}, but this commit is already included in the base branch"
         ));
         return Err(Error::EmptyPatch);
     }