fix(ci): push detached HEAD to master using HEAD:master refspec

The changelog job checks out a specific SHA (detached HEAD) then
commits CHANGELOG.md and tries to push with 'git push origin master'.
Since there is no local branch named 'master', git rejects the push
with 'src refspec master does not match any'.

Fix: use 'git push origin HEAD:master' which explicitly maps the
current detached HEAD to the remote master branch regardless of
local branch state.

.gitea/workflows/auto-tag.yml

@@ -174,7 +174,7 @@ jobs:
           fi
           git add CHANGELOG.md
           git commit -m "chore: update CHANGELOG.md for ${TAG} [skip ci]" || echo "No changes to commit"
-          git push origin master
+          git push origin HEAD:master
           echo "✓ CHANGELOG.md committed to master"
 
       - name: Upload CHANGELOG.md as release asset