python: Sort migrations/management command imports with isort.

This is a preparatory commit for using isort for sorting all of our
imports, merging changes to files where we can easily review the
changes as something we're happy with.

These are also files with relatively little active development, which
means we don't expect much merge conflict risk from these changes.

pgroonga/migrations/0001_enable.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
-from django.db import migrations
 from django.conf import settings
+from django.db import migrations
 
 
 class Migration(migrations.Migration):

pgroonga/migrations/0002_html_escape_subject.py

@@ -1,9 +1,11 @@
 # -*- coding: utf-8 -*-
-from django.db import migrations, connection
+from django.db import connection, migrations
 from django.db.backends.postgresql_psycopg2.schema import DatabaseSchemaEditor
 from django.db.migrations.state import StateApps
+
 from zerver.lib.migrate import do_batch_update
 
+
 def rebuild_pgroonga_index(apps: StateApps, schema_editor: DatabaseSchemaEditor) -> None:
     with connection.cursor() as cursor:
         do_batch_update(cursor, 'zerver_message', ['search_pgroonga'],

pgroonga/migrations/0003_v2_api_upgrade.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
-from django.db import migrations
 from django.conf import settings
+from django.db import migrations
 
 
 class Migration(migrations.Migration):