Checklist

• The bug is reproducible against the latest release or master.
• There are no similar issues or pull requests to fix it yet.

Describe the bug

Ajax request from browser doesn't consider urn which setted up by sub fastapi app.

Steps to reproduce the bug

1. Link admin to sub fastapi app:

from fastapi import FastApi
from sqladmin import Admin

app = FastApi()
subapp = FastApi()
app.mount('/suburn', subapp)

admin = Admin(subapp, base_url='/') 

2. Link any ModelView with relationship with admin which forces ajax request at select list on create page.
3. Click on select list on create page and try to type symbols.

Expected behavior

Ajax should request to uri as: .../suburn/ModelViewName/ajax/...

Actual behavior

Ajax request to uri: .../ModelViewName/ajax/... with skipping suburn.

P.S. Admin page routing is correct with sub app.

Debugging material

In my way:
suburn='/admin'
base_url='/'

[INFO] uvicorn.access: 127.0.0.1:64082 - "GET /admin/enterprise/list HTTP/1.1" 200
[INFO] uvicorn.access: 127.0.0.1:64082 - "GET /admin/enterprise/create HTTP/1.1" 200
[INFO] uvicorn.access: 127.0.0.1:64082 - "GET /enterprise/ajax/lookup?name=company&term=2 HTTP/1.1" 404

Environment

OS:
MacOS 14.4.1

Python:
3.11.8

sqladmin==0.16.1
fastapi==0.110.1

Additional context

I understand that suburn not passed to template ajax, but all another routing work correctly - it confused me.
(I think that we need additional param like sub_url separatly off base_url to specific behavior.)