Push HEAD:master to the AUR rather than a branch name

Cloning a package that does not exist on the AUR yet gives an empty repo
whose initial branch follows the runner's init.defaultBranch, which is not
guaranteed to be master. Verified against the real AUR remote: auth works,
the empty clone yields a .git, and 'git diff --staged --quiet' correctly
reports changes there - so the first publish commits instead of exiting
early with 'nothing to push'.

scripts/push-aur.sh

@@ -61,6 +61,9 @@ fi
 
 version="$(awk -F= '/^pkgver=/{v=$2} /^pkgrel=/{r=$2} END{print v"-"r}' PKGBUILD)"
 git commit -m "Update to ${version}"
-git push -u origin master
+# Push HEAD explicitly rather than a branch name: cloning a package that does
+# not exist on the AUR yet yields an empty repo whose initial branch depends on
+# the runner's init.defaultBranch, which may not be master.
+git push -u origin HEAD:master
 
 echo ":: pushed ${PKGNAME} ${version} to the AUR"