chore: update github action trigger

.github/workflows/preview-theme.yml

@@ -9,16 +9,19 @@ on:
       - "themes/index.js"
   issue_comment:
     types: [edited]
-    branches:
-      - master
-      - theme-preview-script
-      - "themes/index.js"
 
 jobs:
+  comment:
+    if: contains(github.event.comment.html_url, '/pull/')
+    runs-on: ubuntu-latest
+    steps:
+      - name: say hello
+        if: contains(github.event.comment.body, 'Automated Theme Preview')
+        run: |
+          echo say hello
   build:
     runs-on: ubuntu-latest
     name: Install & Preview
-
     steps:
       - uses: actions/checkout@v1
       - uses: bahmutov/npm-install@v1