badge showing "CI: failing", probably wrongly

[noamraph]

Describe the issue

In the main page, the badge shows "CI: failing". When clicking it, I see a failure, but not on the master branch, but on some PR:

This might be because the PR's source branch contains the string "master".

Anyway, I tried adding a "branch" parameter to the image URL, as described here, but then I just see "CI: no status":

It's not a real bug in the product, but it feels much better to use a library which has "build: passing" rather than "build: failling".