ci: pin astral-sh/setup-uv to v8.0.0

Use specific commit hash for reproducible CI runs.

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

Author: amannocci

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
       - uses: actions/checkout@v6
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v8
+        uses: astral-sh/setup-uv@cec208311dfd045dd5311c1add060b2062131d57 # v8.0.0
 
       - name: Run tests
         run: uv run poe test