Add tmate GitHub workflow

.github/workflows/tmate.yml

@@ -0,0 +1,23 @@
+# See https://github.com/mxschmitt/action-tmate
+
+name: tmate
+on:
+  workflow_dispatch:
+    inputs:
+      debug_enabled:
+        type: boolean
+        description: 'Run with tmate debugging enabled (https://github.com/marketplace/actions/debugging-with-tmate)'
+        required: false
+        default: false
+
+jobs:
+  debug:
+    runs-on: ubuntu-latest
+    steps:
+      # Enable tmate debugging of manually-triggered workflows if the input
+      # option was provided
+      - name: Setup tmate session
+        uses: mxschmitt/action-tmate@v3
+        if: ${{ github.event_name == 'workflow_dispatch' && inputs.debug_enabled }}
+        with:
+          limit-access-to-actor: true