release: Fix AUR push to use filtered parent commit

AUR hook validates parent commits too. Use aur/master as parent for the
filtered commit instead of HEAD, so the hook only sees clean history.

Author: jetm

release.sh

@@ -140,9 +140,11 @@ git tag "${new_tag}"
 echo ""
 echo "Pushing to origin and aur..."
 git push origin master
-# AUR rejects subdirectories (.github/). Create a filtered commit for AUR.
+# AUR rejects subdirectories (.github/). Create a filtered commit parented on
+# AUR's current master so the hook only sees clean commits.
 aur_tree=$(git ls-tree HEAD | grep -v '.github' | git mktree)
-aur_commit=$(git commit-tree "${aur_tree}" -p HEAD -m "Release ${new_tag}")
+aur_parent=$(git rev-parse aur/master)
+aur_commit=$(git commit-tree "${aur_tree}" -p "${aur_parent}" -m "Release ${new_tag}")
 git -c push.followTags=false push aur "${aur_commit}:refs/heads/master"
 git -c push.followTags=false push origin "${new_tag}"