migrations: Merge 0517 as a no-op.

Migration 0517 migration was already run as 0497 on `main`, but was
accidentally omitted on 8.x until this point.

Merge the 0517 migration into the migration history.  It is included
as a no-op in `main` because it has already run as 0497.

zerver/migrations/0518_merge.py

@@ -0,0 +1,12 @@
+from django.db import migrations
+
+# See 0517 for the history of this migration merge commit.
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("zerver", "0516_fix_confirmation_preregistrationusers"),
+        ("zerver", "0517_resort_edit_history"),
+    ]
+
+    operations = []