chore(ci): pin astral-sh/setup-uv to v6.7.0

Closes the CodeQL "Unpinned 3rd party Action" warning carried over
from PR #5. Mirrors the pinning convention the other actions in
this workflow already use (actions/checkout@v6.0.2,
actions/setup-python@v6.2.0).

v6.7.0 is the last v6.x release before v7 retired some flags this
workflow relies on; staying on the v6 line matches what CI was
implicitly resolving via @v6.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: aksOps

.github/workflows/ci.yml

@@ -23,7 +23,7 @@ jobs:
           python-version: "3.11"
 
       - name: Set up uv
-        uses: astral-sh/setup-uv@v6
+        uses: astral-sh/setup-uv@v6.7.0
         with:
           # Pin uv version for reproducible CI; bump deliberately when bumping locally.
           version: "0.11.7"