Fix dependabot not able to access firebase token (#35)

Author: DCSBL

.github/workflows/firebase-hosting-pull-request.yml

@@ -1,5 +1,5 @@
 name: Deploy preview on pull request
-on: pull_request
+on: pull_request_target
 jobs:
     build_and_preview:
         if: '${{ github.event.pull_request.head.repo.full_name == github.repository }}'