Support apps with custom label.

tests/test_project/app_with_custom_name/apps.py

@@ -0,0 +1,8 @@
+from __future__ import annotations
+
+from django.apps import AppConfig
+
+
+class DefaultConfig(AppConfig):
+    name = "tests.test_project.app_with_custom_name"
+    label = "my_custom_name"

tests/test_project/app_with_custom_name/migrations/0001_initial.py

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+# Generated by Django 2.2 on 2019-07-29 21:21
+
+from __future__ import annotations
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="A",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                ("int_field", models.IntegerField()),
+                ("char_field", models.CharField(max_length=255)),
+            ],
+        )
+    ]

tests/test_project/app_with_custom_name/models.py

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+from __future__ import annotations
+
+from django.db import models
+
+
+class A(models.Model):
+    int_field = models.IntegerField()
+    char_field = models.CharField(max_length=255)