actions: upload artifacts for stubs & docs

Author: jepler

.github/workflows/build.yml

@@ -66,8 +66,16 @@ jobs:
       working-directory: tests
     - name: Stubs
       run: make stubs -j2
+    - uses: actions/upload-artifact@v2
+      with:
+        name: stubs
+        path: circuitpython-stubs*
     - name: Docs
       run: sphinx-build -E -W -b html . _build/html
+    - uses: actions/upload-artifact@v2
+      with:
+        name: docs
+        path: _build/html
     - name: Translations
       run: make check-translate
     - name: New boards check