2.32.3 does not load system CA certificates when using an Adapter

<!-- Summary. -->

Given this snippet:

```py
from requests.adapters import HTTPAdapter
from requests import Session
from urllib3 import PoolManager
from urllib3 import ProxyManager
from urllib3.util.ssl_ import create_urllib3_context


class AFIPAdapter(HTTPAdapter):
    """An adapter with reduced security so it'll work with AFIP."""

    def init_poolmanager(self, *args, **kwargs) -> PoolManager:
        context = create_urllib3_context(ciphers="AES128-SHA")
        # context.load_default_certs()
        kwargs["ssl_context"] = context
        return super().init_poolmanager(*args, **kwargs)

    def proxy_manager_for(self, *args, **kwargs) -> ProxyManager:
        context = create_urllib3_context(ciphers="AES128-SHA")
        # context.load_default_certs()
        kwargs["ssl_context"] = context
        return super().proxy_manager_for(*args, **kwargs)


session = Session()
session.mount("https://servicios1.afip.gov.ar", AFIPAdapter())
session.get("https://servicios1.afip.gov.ar/wsfev1/service.asmx?WSDL")
```

On `requests==2.31.0`, this works fine (e.g.: system CAs are loaded by default).

As of `2.32.2`, the system CAs are no longer loaded by default, and the commented `context.load_default_certs()` lines need to be included too.

## Expected Result

Above snippet should work; system CAs should be loaded.

## Actual Result

Above snippet fails with:

```
requests.exceptions.SSLError: HTTPSConnectionPool(host='servicios1.afip.gov.ar', port=443): Max retries exceeded with url: /wsfev1/service.asmx?WSDL (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1000)
```

## System Information

    $ python -m requests.help

```json
{
  "chardet": {
    "version": null
  },
  "charset_normalizer": {
    "version": "3.3.2"
  },
  "cryptography": {
    "version": "39.0.2"
  },
  "idna": {
    "version": "3.7"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.12.3"
  },
  "platform": {
    "release": "6.9.3-0-edge",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "30000080",
    "version": "23.2.0"
  },
  "requests": {
    "version": "2.32.3"
  },
  "system_ssl": {
    "version": "30300000"
  },
  "urllib3": {
    "version": "2.2.1"
  },
  "using_charset_normalizer": true,
  "using_pyopenssl": true
}
```

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## Further context

https://github.com/psf/requests/pull/6710#issuecomment-2137799723


Hi @WhyNotHugo, I think this is a duplicate of #6730 which was opened after your original comment. We'll track progress there.

Sorry, forgot to double-check.

@WhyNotHugo did you solve it ? I'm struggling with the same

```
urllib3 = "^1.26.14"
fintech = "^7.5.1"
pyopenssl = "^22.0.0"
cryptography = "^35.0.0"
```

since I updated cryptography

@alesisjoan Either use dependency `"requests!=2.32.0,!=2.32.1,!=2.32.2",` or explicitly load default certs: https://github.com/WhyNotHugo/django-afip/blob/8ea6dbd79d9cfe52409d9bbf3d61069ea8efbdb0/django_afip/clients.py#L44-L57

Hi Hugo!
Yep, it was something with requests library.

In my case it was using 2.32 so I force a  downgrade to 2.25.1

Muchas gracias!

El mié., 3 de julio de 2024 12:09, Hugo ***@***.***> escribió:

> @alesisjoan <https://github.com/alesisjoan> Either use dependency
> "requests!=2.32.0,!=2.32.1,!=2.32.2", or explicitly load default certs:
> https://github.com/WhyNotHugo/django-afip/blob/8ea6dbd79d9cfe52409d9bbf3d61069ea8efbdb0/django_afip/clients.py#L44-L57
>
> —
> Reply to this email directly, view it on GitHub
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