🛠 fix: Adapter overwrite passed-in retry

[tomy0000000]

According to the API reference of max_retries of requests.adapters.HTTPAdapter

The maximum number of retries each connection should attempt. Note, this applies only to failed DNS lookups, socket connections and connection timeouts, never to requests where data has made it to the server. By default, Requests does not retry failed connections. If you need granular control over the conditions under which we retry a request, import urllib3’s Retry class and pass that instead.

A widely used example can be found in this StackOverflow answer and is also under review in #6258.

However, the current source code does not really accept the passed-in Retry instance. Instead, it will silently discard and replace it with the default Retry instance.

This 2-line fix intends to fix the bug and restore its behavior to expect.

[sigmavirus24]

You haven't provided evidence that this isn't working. The from_int classmethod returns the Retry instance if it's already a Retry

[tomy0000000]

My mistake. Turns out I used the wrong scheme (http:// should be https://) when mounting in my previous test.

Closing this PR, but do look into #6258 and get it merged. Took me a while to get this snippet that should've been in official docs.