Add mkdir step before cp (#799)

Author: mingjerli

.github/workflows/demos.yml

@@ -15,7 +15,7 @@ jobs:
         with:
           fetch-depth: 0 # otherwise, there would be errors pushing refs to the destination repository.
       - name: "Copy demo notebooks to top level demos folder"
-        run: cp -R examples/use_cases/* demos/ && cp examples/tutorials/00_api_basics.ipynb demos/
+        run: mkdir demos/ && cp -R examples/use_cases/* demos/ && cp examples/tutorials/00_api_basics.ipynb demos/
 
       - name: "Regex out the NBVAL_SKIP and NBVAL_IGNORE_OUTPUT comments"
         run: |