Update GH workflow to ignore MongoDB startup.

Author: marc0der

.github/workflows/pr.yml

@@ -4,11 +4,6 @@ on: pull_request_target
 jobs:
   build:
     runs-on: ubuntu-latest
-    services:
-      mongodb:
-        image: mongo:3.2
-        ports:
-          - 27017:27017
     steps:
       - name: Checkout source code
         uses: actions/checkout@v2