gha: Add push trigger

.github/workflows/purge-readme-image-cache.yml

@@ -1,6 +1,7 @@
 name: Purge image cache
 
 on:
+  push:
   schedule:
     - cron: '4 18 * * *'
 
@@ -9,8 +10,8 @@ jobs:
     runs-on: ubuntu-18.04
     steps:
 
-    - run: |
-        IMAGE_LIST=$(curl -sL https://github.com/${GITHUB_REPOSITORY} | \
-          grep -oE '<img src="https?://camo.githubusercontent.com/[^"]+' | \
-          sed -e 's/<img src="//')
-        echo ${IMAGE_LIST} | xargs -I % curl -sX PURGE %
+    - run: >
+        curl -sL https://github.com/${GITHUB_REPOSITORY} |
+        grep -oE '<img src="https?://camo.githubusercontent.com/[^"]+' |
+        sed -e 's/<img src="//' |
+        xargs -I % curl -sX PURGE %