improve github ci

.github/workflows/ci.yaml

@@ -1,12 +1,16 @@
 name: CI
 
-on: [ push, pull_request ]
+on:
+  push:
+    branches: ['main']
+  pull_request:
 
 jobs:
   ci:
     name: CI
     runs-on: ubuntu-20.04
     strategy:
+      fail-fast: false
       matrix:
         php-versions: [ '7.4', '8.0', '8.1', '8.2' ]
 
@@ -23,10 +27,12 @@ jobs:
         run: find -L . -path ./vendor -prune -o -type f -name '*.php' -print0 | xargs -0 -n 1 -P $(nproc) php -l
 
       - name: Get composer cache directory
+        # https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter
         id: composer-cache
         run: echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - name: Cache composer
+        # https://github.com/shivammathur/setup-php/tree/v2/#cache-composer-dependencies
         uses: actions/cache@v3
         with:
           path: ${{ steps.composer-cache.outputs.dir }}