Don't build on push and PR.

.github/workflows/ci.yml

@@ -4,7 +4,14 @@
 # (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
 
 name: CI
-on: [ push, pull_request ]
+on:
+  push:
+    branches:
+      - master
+      - develop
+  pull_request:
+  release:
+    types: [published, created, edited]
 jobs:
   ubuntu-focal:
     runs-on: ubuntu-20.04