Fix changelog workflow (#2604)

Fix the workflow to make sure it runs on pull requests against forked branches and also don't run on l10_master and dependabot branches

.github/workflows/changelog-check.yml

@@ -2,24 +2,26 @@ name: Changelog in sync for packages
 
 on:
   push:
-    branches-ignore:
-      - "l10n_master"
-      - "dependabot/**"
+    branches:
+      - master
+  pull_request:
 jobs:
   test:
     runs-on: ubuntu-latest
 
     steps:
       - uses: actions/checkout@v1
-
       - name: Setup Node.js 14.x
         uses: actions/setup-node@v1
         with:
           node-version: 14.x
-
       - name: Install and run changelog check
-        run: |
-          npm ci
-          npm run changelog:check
+        run:
+          if [[ $GITHUB_HEAD_REF =~ dependabot || $GITHUB_HEAD_REF == "l10n_master" ]]; then
+          echo "Skipping running changelog check";
+          else
+          npm ci;
+          npm run changelog:check;
+          fi
         env:
           CI: true