fix: only run Asana jobs if the secrets are present

This avoids failures when running on PRs from forks.

We do it in this convoluted way because you can't access secrets
directly from `if` blocks: actions/runner#520

.github/workflows/asana.yml

@@ -29,9 +29,17 @@ on:
         required: false
         description: GitHub secret that Asana uses to fetch PR information.
 jobs:
+  check-for-secrets:
+    runs-on: ubuntu-latest
+    outputs:
+      has-asana-token: ${{ secrets.asana-token != '' }}
+      has-github-secret: ${{ secrets.github-secret != '' }}
+    steps:
+      - run: true
   move-to-merged-asana-ticket-job:
     runs-on: ubuntu-latest
-    if: inputs.merged-section != '' && github.event.pull_request.merged == true && github.actor != 'dependabot[bot]' 
+    needs: check-for-secrets
+    if: inputs.merged-section != '' && needs.check-for-secrets.output.has-asana-token == 'true' && github.event.pull_request.merged == true && github.actor != 'dependabot[bot]'
     steps:
       - name: Move ticket on merge
         uses:  mbta/[email protected]
@@ -42,7 +50,8 @@ jobs:
           mark-complete: ${{ inputs.complete-on-merge }}
   move-to-in-review-asana-ticket-job:
     runs-on: ubuntu-latest
-    if: inputs.review-section != '' && github.event.action == 'review_requested' && github.actor != 'dependabot[bot]'
+    needs: check-for-secrets
+    if: inputs.review-section != '' && needs.check-for-secrets.output.has-asana-token == 'true' && github.event.action == 'review_requested' && github.actor != 'dependabot[bot]'
     steps:
       - name: Move ticket on review requested
         uses:  mbta/[email protected]
@@ -52,8 +61,9 @@ jobs:
           target-section: ${{ inputs.review-section }}
   create-asana-attachment-job:
     runs-on: ubuntu-latest
+    needs: check-for-secrets
     name: Create pull request attachments on Asana tasks
-    if: inputs.attach-pr && github.actor != 'dependabot[bot]'
+    if: inputs.attach-pr && needs.check-for-secrets.output.has-github-secret == 'true' && github.actor != 'dependabot[bot]'
     steps:
       - name: Create pull request attachments
         uses: Asana/[email protected]