fix(decision): cleanup temporary uv lockfiles

This was causing problems, as the `worker` user was trying to create the
same file, but it already existed and was owned by `root`.

Ensure we don't leave these lying around.

taskcluster/docker/decision/system-setup.sh

@@ -18,3 +18,4 @@ apt-get clean
 apt-get autoclean
 rm -rf /var/lib/apt/lists/
 rm -rf /setup
+rm /tmp/uv-*.lock