Replace master references in workflow definition with the 'on' section from jaraco/skeleton.

Author: jaraco

.github/workflows/main.yml

@@ -1,10 +1,15 @@
 name: tests
 
 on:
+  merge_group:
   push:
-    branches: [ master ]
+    branches-ignore:
+    # temporary GH branches relating to merge queues (jaraco/skeleton#93)
+    - gh-readonly-queue/**
+    tags:
+    # required if branches-ignore is supplied (jaraco/skeleton#103)
+    - '**'
   pull_request:
-    branches: [ master ]
 
 jobs:
   build: