BCDA-8639: Fix cron issue in workflow (#223)

## 🎫 Ticket

https://jira.cms.gov/browse/BCDA-8639

## 🛠 Changes

Added env var that can be set when a workflow is run from a cron
expression.

## ℹ️ Context

Previously the input workflow env var was not accessible during a cron
execution. See failure here:
https://github.com/CMSgov/bcda-static-site/actions/runs/12743251972

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## 🧪 Validation

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.github/workflows/508_compliance_check.yml

@@ -19,9 +19,13 @@ jobs:
     name: Compliance Check
     runs-on: self-hosted
     steps:
+      - name: Set Target Base
+        id: target-base
+        run: |
+          echo "TARGET_BASE_URL=${{ inputs.target_host || 'https://stage.bcda.cms.gov' }}" >> "$GITHUB_OUTPUT"
       - name: Run Axe Check
         env:
-          TARGET_BASE_URL: ${{ inputs.target_host }}
+          TARGET_BASE_URL: ${{ steps.target-base.outputs.TARGET_BASE_URL }}
         run: |
           TARGETS_TO_SCAN="${TARGET_BASE_URL}"
           TARGETS_TO_SCAN="${TARGETS_TO_SCAN} ${TARGET_BASE_URL}/guide.html"