fix: downgrade setup-python action to v5

setup-python@v6 doesn't exist yet, causing workflow failures.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: graycreate

.github/workflows/release.yml

@@ -685,7 +685,7 @@ ${formatted}"
       uses: actions/checkout@v5
 
     - name: Set up Python
-      uses: actions/setup-python@v6
+      uses: actions/setup-python@v5
       with:
         python-version: '3.x'