fix(ci): use refs/tags/ prefix to avoid ambiguity between branch and tag names

CI_TAG がブランチ名とタグ名で同一になるため git push が ambiguous になる問題を修正。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: highemerly

.github/workflows/check-upstream.yml

@@ -150,9 +150,9 @@ jobs:
           # CI ブランチをpush
           git push origin "$CI_TAG"
 
-          # actions-v4.5.9-YYYYMMDDHHMMSS タグを打つ
+          # actions-v4.5.9-YYYYMMDDHHMMSS タグを打つ (refs/tags/ を明示してブランチ名と衝突回避)
           git tag "$CI_TAG"
-          git push origin "$CI_TAG" --tags
+          git push origin "refs/tags/$CI_TAG"
 
           # handon-production を force update
           git push origin "HEAD:handon-production" --force