Fix check for lazily evaluated objects

[laymonage]

_delegated_text no longer exists in Django as of https://github.com/django/django/commit/ee36e101e8f8c0acde4bb148b738ab7034e902a0

This is also how Django internally checks for lazily-translated strings (search for Promise in its codebase), e.g.

• https://github.com/django/django/blob/531f557f9238b8f2e5032e569cf36f0c05bb4043/django/utils/encoding.py#L31-L33
• https://github.com/django/django/blob/531f557f9238b8f2e5032e569cf36f0c05bb4043/django/utils/encoding.py#L85-L87
• https://github.com/django/django/blob/531f557f9238b8f2e5032e569cf36f0c05bb4043/django/db/models/fields/__init__.py#L315-L317