proxy params is changed for httpx

[ainamori]

Describe the bug

Key name for proxy params is wrong.

To Reproduce

Steps to reproduce the behavior:

1. Create instance with proxy param like this.

        myTeamsMessage = pymsteams.async_connectorcard(
            hookurl="<MS Teams webhook url>",
            http_proxy="http://proxy.example.com:8080",
            https_proxy="http://proxy.example.com:8080",
        )

2. run this programs.
3. it appears the following logs like this.

ValueError: Proxy keys should use proper URL forms rather than plain scheme strings. Instead of "http", use "http://"

---

• See the httpx proxy specification.
  • https://www.python-httpx.org/advanced/#http-proxying

[rveachkc]

Thanks for looking into this, and closing out