Moved the skip command to an env variable

.github/workflows/deploy-pr-preview.yaml

@@ -10,6 +10,7 @@ env:
   PR_PREVIEW_SUBDOMAIN: pr-${{github.event.pull_request.number}}-preview
   PR_PREVIEW_DEPLOY_LOG_URL: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}
   PR_PREVIEW_BUCKET: s3://khpreview.dea.ga.gov.au
+  PR_PREVIEW_SKIP_COMMAND: "[no preview]"
 
 permissions:
   id-token: write # For requesting the JWT used by OIDC Authentication
@@ -20,9 +21,9 @@ jobs:
   pr-preview:
     runs-on: ubuntu-latest
     if: |
-      !contains(github.event.head_commit.message, '[skip preview]') &&
-      !contains(github.event.pull_request.title, '[skip preview]') &&
-      !contains(github.event.pull_request.body, '[skip preview]')
+      !contains(github.event.head_commit.message, '${{ env.PR_PREVIEW_SKIP_COMMAND }}') &&
+      !contains(github.event.pull_request.title, '${{ env.PR_PREVIEW_SKIP_COMMAND }}') &&
+      !contains(github.event.pull_request.body, '${{ env.PR_PREVIEW_SKIP_COMMAND }}')
 
     strategy:
       matrix: