storage: Fix type annotation of content.
storage: Fix type annotation of content.

Currently django-stubs expects `File` to be generic, this is not yet
supported. We quote it for now before django-stubs gets integrated.

TODO: unquote this in the future.

See also: https://github.com/typeddjango/django-stubs/issues/1061#issuecomment-1185995937.

Signed-off-by: Zixuan James Li <74923aee05c23ca90566381b5d6b0cd9451b6054@gmail.com>

zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip,andersk/zulip,andersk/zulip,rht/zulip,zulip/zulip,rht/zulip,rht/zulip,rht/zulip,zulip/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip