Gitea API has changed and now 404 for branch search gives back a
shorter error message [1]. tools/delete_*_branch.py script has to
be updated to only match for the new message.
[1] ERROR: (404): {"errors":null,"message":"not found","url":"https://opendev.org/api/swagger"}
Change-Id: I99813e63f8d9f04557da9a37bb41a30d21075701
Signed-off-by: Előd Illés <elod.illes@est.tech>