* fix: Dont create inward SLE against SI unless is internal customer enabled
- Check if is internal customer enabled apart from target warehouse
- Test to check if inward SLE is made if target warehouse is accidentally set but customer is not internal
* test: Use internal customer for delivery of bundle items to target warehouse
- created `create_internal_customer` util
- reused it in delivery note and sales invoice tests
- use internal customer for target warehouse test in delivery note