add action to debug homebrew on GitHub runners

Author: jdtournier

.github/workflows/tmate_macos.yml

@@ -0,0 +1,9 @@
+name: CI
+on: [push]
+jobs:
+  build:
+    runs-on: macos-latest
+    steps:
+    - uses: actions/checkout@v1
+    - name: Setup tmate session
+      uses: mxschmitt/action-tmate@v1