ci: pin astral-sh/setup-uv to v8.1.0 (no sliding-major tag exists)

Last push failed with:
  Unable to resolve action astral-sh/setup-uv@v8, unable to find version v8

Unlike actions/* and docker/* which publish a sliding major-version
tag (v6, v7, etc.) that points at the latest within the major,
astral-sh/setup-uv only publishes specific version tags (v8.0.0,
v8.1.0).  Pinning to the exact tag.

Future bumps need to be manual when astral cuts a new minor — small
cost given this is a single dep on the workflow.

Author: Sbussiso

.github/workflows/deploy.yml

@@ -13,7 +13,12 @@ jobs:
       - uses: actions/checkout@v5
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v8
+        # astral-sh/setup-uv doesn't publish sliding major-version
+        # tags (v7, v8 etc.) the way actions/* and docker/* do — only
+        # specific versions like v8.1.0.  Pin to the exact tag and
+        # bump manually when there's a reason to.  v8.x is the first
+        # Node.js 24-ready major.
+        uses: astral-sh/setup-uv@v8.1.0
 
       - name: Set up Python
         run: uv python install 3.12