debug(ci): set env variables only for storybook build

.github/workflows/deploy-storybook.yaml

@@ -40,9 +40,6 @@ jobs:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
     runs-on: ubuntu-latest
-    env:
-      GH_PAGES: true
-      BASE_URL: "/nimbus-gui/"
     needs: cache-dependencies
     steps:
       - uses: actions/checkout@v2
@@ -64,7 +61,7 @@ jobs:
       - name: Install Playwright
         run: npx playwright install --with-deps
       - name: Build Storybook
-        run: yarn build-storybook --quiet
+        run: GH_PAGES=true BASE_URL="/nimbus-gui/" yarn build-storybook --quiet
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v2
         with: