Update locking workflow

The old workflow seems to not be working anymore. This repo looks like the natural successor.

I upped the time for locking to 90 days since ipywidgets has a slower cadence than many other Jupyter projects.

Author: jasongrout

.github/lock.yml

@@ -0,0 +1,17 @@
+name: 'Lock Closed Threads'
+
+on:
+  schedule:
+    - cron: '0 0 * * *'
+
+jobs:
+  lock:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v2
+        with:
+          github-token: ${{ github.token }}
+          issue-lock-inactive-days: '90'
+          issue-lock-labels: 'resolved-locked'
+          pr-lock-inactive-days: '90'
+          pr-lock-labels: 'resolved-locked'