Add secret validation

Author: roji

.github/workflows/TestSqlServer.yaml

@@ -39,6 +39,15 @@ jobs:
           --health-timeout=5s
 
     steps:
+      # Note that the secret is required for the SQL Server service to start above, and that happens before any steps.
+      # We still have this step with always() (so it doesn't get skipped if the service failed to start) to help debug
+      # issues.
+      - name: Check that secrets.MSSQL_SA_PASSWORD2 exists
+        if: always() && ${{ secrets.MSSQL_SA_PASSWORD2 == '' }}
+        run: |
+          echo "::error::Missing secret: MSSQL_SA_PASSWORD2"
+          exit 1
+
       - name: Checkout
         uses: actions/checkout@v6