SSL: WRONG_VERSION_NUMBER

Hi,

I'm trying to enable allow_self_approval, but I'm facing this error :
```
20:36:49.279 [ConfigProxy] debug: PROXY WEB /hub/signup to http://jupyterhub:8081
[E 2024-02-22 20:36:49.526 JupyterHub nativeauthenticator:357] [SSL: WRONG_VERSION_NUMBER] wrong version number (_ssl.c:1007)

```

In the following, my configuration :

```
c.NativeAuthenticator.allow_self_approval_for = '[^@]+@hotmail\.com$'
c.NativeAuthenticator.secret_key = "your-arbitrary-key-your-arbitrary-key-your-arbitrary-key-your"
c.NativeAuthenticator.self_approval_email = (
"user.one@comp.fr",
"approval_link",
"email body including https://hotmail.com{approval_url}",
)
c.NativeAuthenticator.self_approval_server = {
'url': 'smtp.comp.fr',
'usr': 'user.one',
'pwd': '123456789'
}
```

Start at the nativeauthenticator:357 log entry and inspect how the self-approval email configuration reaches the configured smtp.comp.fr server. Reproduce the signup flow with allow_self_approval enabled, then determine what configuration or connection change prevents [SSL: WRONG_VERSION_NUMBER] and allows the approval email to be sent.

Written by the indexing model from the issue text.