Fix NPM release workflow to use micromamba environment (#617)

The jlpm command wasn't available because commands weren't running
in the micromamba environment where JupyterLab is installed. Use
'micromamba run -n ipympl-release' to execute commands in the correct
environment.

Fixes #616

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: ianhi

.github/workflows/release.yml

@@ -34,8 +34,9 @@ jobs:
 
     - name: Publish the NPM package
       run: |
-        jlpm install && jlpm build
-        npm publish
+        micromamba run -n ipympl-release jlpm install
+        micromamba run -n ipympl-release jlpm build
+        micromamba run -n ipympl-release npm publish
       env:
         NODE_AUTH_TOKEN: ${{ secrets.NPM_TOKEN }}
         PRE_RELEASE: ${{ github.event.release.prerelease }}