Unable to delete a branch: missing delete-ref permission

Problem Solution
git push origin :dev

results in

remote:  ! [remote rejected] dev
(User bruno does not have delete-ref privilege
for reference refs/heads/dev.)

Grant the permission to delete a repo in the graph depot:

p4 grant-permission -u bruno -p delete-ref -d gD1

See p4 grant-permission in Helix Core Command-Line (P4) Reference.