Use env vars in GHA dependabot changelog (#14772)

.github/workflows/dependabot_changelog.yml

@@ -20,8 +20,11 @@ jobs:
         with:
           ref: ${{ github.event.pull_request.head.ref }}
       - name: Write, commit and push changelog
+        env:
+          PR_TITLE: ${{ github.event.pull_request.title }}
+          PR_NUMBER: ${{ github.event.pull_request.number }}
         run: |
-          echo "${{ github.event.pull_request.title }}." > "changelog.d/${{ github.event.pull_request.number }}".misc
+          echo "${PR_TITLE}." > "changelog.d/${PR_NUMBER}".misc
           git add changelog.d
           git config user.email "github-actions[bot]@users.noreply.github.com"
           git config user.name "GitHub Actions"

changelog.d/14772.misc

@@ -0,0 +1 @@
+Change GHA CI job to follow best practices.