Previously, if no branch was explicitly specified for a workflow, it
defaulted to the default branch of the repo. This worked fine for
workflows that were triggered on push, but it prevented showing badges
for workflows that only run on tags, or on schedule - since they do not
run on a specific branch.
Thus, relax the conditions, and if no branch is specified, just return
the latest run of the given workflow. If one is specified, *then*
restrict it to said branch.
Fixes #3487.
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>
(cherry picked from commit d6915f4d5f)
