ci: only run changelog checker in PR (#2370)

Author: SteveLauC

.github/workflows/check_new_changelog.yml

@@ -0,0 +1,18 @@
+name: Check new CHANGELOGs
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: read 
+
+jobs:
+  check_new_changelog:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: check new CHANGELOG
+        uses: ./.github/actions/check_new_changelog

.github/workflows/ci.yml

@@ -16,15 +16,6 @@ env:
   MSRV: 1.69.0
 
 jobs:
-  check_new_changelog:
-    runs-on: ubuntu-20.04
-    steps:
-      - name: checkout
-        uses: actions/checkout@v4
-
-      - name: check new CHANGELOG
-        uses: ./.github/actions/check_new_changelog
-
   macos:
     runs-on: macos-13
     env: