Show "exec" todos in the list of rebase todos

Unfortunately it isn't possible to delete them. This would often be useful, but
our todo rewriting mechanisms rely on being able to find todos by some
identifier (hash for pick, ref for update-ref), and exec todos don't have a
unique identifier.

pkg/commands/git_commands/commit_loader.go

@@ -344,6 +344,8 @@ func (self *CommitLoader) getRebasingCommits(rebaseMode enums.RebaseMode) []*mod
 	for _, t := range todos {
 		if t.Command == todo.UpdateRef {
 			t.Msg = t.Ref
+		} else if t.Command == todo.Exec {
+			t.Msg = t.ExecCommand
 		} else if t.Commit == "" {
 			// Command does not have a commit associated, skip
 			continue