swap to npm in ci, pnpm wasn't supported

Author: matthew-gill

.github/workflows/deploy-storybook.yml

@@ -16,4 +16,4 @@ jobs:
       uses: bitovi/github-actions-storybook-to-github-pages@v1.0.3
       with:
         path: storybook-static
-        install_command: pnpm i
+        install_command: npm i