Steps to reproduce

• Create a Scratch Org using the given definition file
  sf org create scratch --definition-file config/project-scratch-def.json --alias myAlias --set-default --target-dev-hub MyHub

• Create an Account
  sf data create record --sobject Account --values "Name=Acme" -o myAlias

• Create a User with the Platform License and the Standard Platform License Profile using the UI

• Change the ApprovalWorkflow string {{PLATFORM_USER_USERNAME}} with the username of the user just created

• Deploy the metadata
  sf project deploy start -o myAlias

• Assign the PermissionSet Approval_Flow_Permissions to the user created 2 steps above