Fix docs GHA workflow since migrating to uv

The command is `uv sync`, not `uv install`.

Author: caleb531

.github/workflows/docs.yml

@@ -30,5 +30,5 @@ jobs:
           path: .cache
           restore-keys: |
             mkdocs-material-
-      - run: uv install --group docs
+      - run: uv sync --group docs
       - run: uv run mkdocs gh-deploy --force