meta: move if condition on workflow to steps

Provisional measure due to "Unexpected value 'if'" error. See https://github.community/t5/GitHub-API-Development-and/jobs-lt-job-id-gt-if-not-working/m-p/28980

.github/workflows/pull_request_triage.yml

 on: pull_request
 name: Triage Pull Request
 jobs:
-  mainJob:
+  triage:
     name: Triage
-    if: github.event.action == 'opened' || github.event.action == 'synchronize'
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
       uses: actions/checkout@master
+      if: github.event.action == 'opened' || github.event.action == 'synchronize'
     - name: Analyze and triage
       uses: ohmyzsh/github-actions/pull-request-triage@master
       env: