fix: drop unused type parameter C from Jobs::get_mut — radicle-job

Signed-off-by: Lars Wirzenius liw@liw.fi

     R: ReadRepository + SignRepository + cob::Store<Namespace = NodeId>,
 {
     /// Get a [`JobMut`], given its [`JobId`] identifier.
     pub fn get_mut<'g, C>(&'g mut self, id: &JobId) -> Result<JobMut<'a, 'g, R>, store::Error> {
     pub fn get_mut<'g>(&'g mut self, id: &JobId) -> Result<JobMut<'a, 'g, R>, store::Error> {
         let job = self
             .raw
             .get(id.as_object_id())?