Fix the URL of the "This branch is now known as <name>" links

Most recently seen in
gitgitgadget/git#1405 (comment),
the URLs pointing to the maintainer's branches reflecting the current PR
are bogus: Instead of the correct
https://github.com/gitster/git/commits/pw/rebase-no-reflog-action, the
forward slash between `gitster` and `git` is replaced with a `.`.

This bug was introduced some time between February 10th 2022
(gitgitgadget/git#1140 (comment))
and February 15t 2022
(gitgitgadget/git#1142 (comment)).

We could now simply replace the `.` by a `/`, but that would introduce
_another_ problem: as a lottery factor exercise, Git is currently
maintained by an interim maintainer and therefore the maintainer
branches in https://github.com/gitster/git aren't updated at all.

Let's side-step that problem completely by using URLs pointing to the
branches that are mirrored into https://github.com/gitgitgadget/git
(which are currently mirrored from https://github.com/ttaylorr/git, i.e.
from the interim maintainer's personal fork).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

lib/ci-helper.ts

@@ -317,7 +317,7 @@ export class CIHelper {
 
         // Identify branch in maintainer repo
         const maintainerBranch = `refs/remotes/${this.config.repo.maintainerBranch}/`;
-        const maintainerRepo = `${this.config.repo.maintainerBranch}.${this.config.repo.name}`;
+        const maintainerRepo = `${this.config.repo.owner}/${this.config.repo.name}`;
 
         let gitsterBranch: string | undefined =
             await git(["for-each-ref", `--points-at=${tipCommitInGitGit}`,