ngettext_lazy result doesn't support `.format`

[patrick]

I was trying to use ngettext_lazy in combination with str.format and I discovered that it doesn't actually work,
here's a test script that you can try with latest django:

import os

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "translation.settings")

import django  # noqa

django.setup()

from django.utils.translation import ugettext_lazy, ngettext_lazy  # noqa

singular_string = ugettext_lazy("this {name} will be translated")
plural_string = ngettext_lazy(
    singular="{total} string will be translated",
    plural="{total} strings will be translated",
    number="total",
)

a = singular_string.format(name="string")

b = plural_string.format(total=2)

print()

print("a:", a)
print("b:", b)

This is the output:

~/D/p/django-ngettext-lazy pipenv run python example.py

a: this string will be translated
b:

EDIT: added a patch here:

​https://github.com/django/django/pull/10691