Refactor gitPush function to handle existing remote branches

pkg/github/bumper/bumper.go

@@ -110,7 +110,8 @@ func gitPush(remote, remoteBranch string, repo *git.Repository, auth transport.A
 			RemoteName: forkRemoteName,
 			RefSpecs:   []config.RefSpec{config.RefSpec(fmt.Sprintf("HEAD:%s", remoteBranch))},
 			Auth:       auth,
-		}); err != nil {
+			// Do not fail if the remote branch is already up-to-date
+		}); err != nil && err != git.NoErrAlreadyUpToDate {
 			return fmt.Errorf("push to remote: %w", err)
 		}
 	} else {