Disable wpgu feature in document CI workflow

`wgpu` takes a long time to document otherwise.

.github/workflows/document.yml

@@ -13,7 +13,8 @@ jobs:
     - name: Generate documentation
       run: |
         RUSTDOCFLAGS="--cfg docsrs" \
-          cargo doc --no-deps --all-features \
+          cargo doc --no-deps --no-default-features \
+          --features image-without-codecs,svg,canvas,qr_code,markdown,highlighter,lazy,tokio \
           -p futures-core \
           -p iced_core \
           -p iced_highlighter \