Replace lock bot with GitHub Action

The lock bot Github app is not working anymore.

.github/workflows/lock.yml

@@ -0,0 +1,32 @@
+name: Lock
+
+# yamllint disable-line rule:truthy
+on:
+  schedule:
+    - cron: "0 * * * *"
+
+jobs:
+  lock:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: dessant/lock-threads@v2.0.1
+        with:
+          github-token: ${{ github.token }}
+          issue-lock-inactive-days: "30"
+          issue-exclude-created-before: "2020-10-01T00:00:00Z"
+          issue-exclude-labels: ""
+          issue-lock-labels: ""
+          issue-lock-comment: >
+            This thread has been automatically locked since there has not been
+            any recent activity after it was closed. Please open a new issue for
+            related bugs.
+          issue-lock-reason: ""
+          pr-lock-inactive-days: "7"
+          pr-exclude-created-before: "2020-10-01T00:00:00Z"
+          pr-exclude-labels: ""
+          pr-lock-labels: ""
+          pr-lock-comment: >
+            This thread has been automatically locked since there has not been
+            any recent activity after it was closed. Please open a new issue for
+            related bugs.
+          pr-lock-reason: ""