Fix: include db_index caveat in squashed migrations (#8292)

src/documents/migrations/0015_add_insensitive_to_match_squashed_0018_auto_20170715_1712.py

@@ -1,6 +1,7 @@
 # Generated by Django 4.2.13 on 2024-06-28 17:57
 
 import django.db.models.deletion
+from django.conf import settings
 from django.db import migrations
 from django.db import models
 
@@ -43,7 +44,7 @@ class Migration(migrations.Migration):
             name="content",
             field=models.TextField(
                 blank=True,
-                db_index=True,
+                db_index=("mysql" not in settings.DATABASES["default"]["ENGINE"]),
                 help_text="The raw, text-only data of the document.  This field is primarily used for searching.",
             ),
         ),