ci: make step conditions more structured

Either have a step always be executed, be executed for prod or be
executed for a PR (staging) and use the same conditions for each of
these cases.

.forgejo/workflows/deploy.yaml

@@ -39,12 +39,13 @@ jobs:
           fetch-depth: 0 # pull full history for page lastmod by git commit date
 
       - name: Build website - prod
+        if: (github.event_name == 'push' || github.event_name == 'schedule') && github.ref_name == 'main'
         run: |
           ./fetch-calendar.sh
           hugo
 
       - name: Build website - staging
-        if: github.ref_name != 'main'
+        if: github.event_name == 'pull_request'
         run: |
           sed -i "s#baseURL = 'https://hamburg.ccc.de/'#baseURL = 'https://staging.hamburg.ccc.de/pr${{ github.event.pull_request.number }}/'#" hugo.toml
           sed -i "s#index = true#index = false#" hugo.toml
@@ -53,7 +54,6 @@ jobs:
           hugo --buildFuture
 
       - name: Deploy - Prepare keys
-        if: github.event_name == 'push' || github.event_name == 'pull_request' || github.event_name == 'schedule'
         run: |
           echo "${{ secrets.SSH_DEPLOY_KEY }}" > deploykey.priv
           chmod 400 deploykey.priv