Deprecation warnings with urllib3 1.26.13

[emosenkis]

Consider requiring urllib3 < 1.26.13 until the deprecated calls are removed.

/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/plaid/api_client.py:769: in __call__
    return self.callable(self, *args, **kwargs)
/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/plaid/api/plaid_api.py:6377: in __item_public_token_exchange
    return self.call_with_http_info(**kwargs)
/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/plaid/api_client.py:831: in call_with_http_info
    return self.api_client.call_api(
/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/plaid/api_client.py:406: in call_api
    return self.__call_api(resource_path, method,
/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/plaid/api_client.py:214: in __call_api
    content_type = response_data.getheader('content-type')
/opt/hostedtoolcache/Python/3.9.15/x64/lib/python3.9/site-packages/plaid/rest.py:38: in getheader
    return self.urllib3_response.getheader(name, default)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <urllib3.response.HTTPResponse object at 0x7f324d7c2dc0>
name = 'content-type', default = None

    def getheader(self, name, default=None):
>       warnings.warn(
            "HTTPResponse.getheader() is deprecated and will be removed "
            "in urllib3 v2.1.0. Instead use HTTResponse.headers.get(name, default).",
            category=DeprecationWarning,
            stacklevel=2,
        )
E       DeprecationWarning: HTTPResponse.getheader() is deprecated and will be removed in urllib3 v2.1.0. Instead use HTTResponse.headers.get(name, default).

[phoenixy1]

thanks for filing! I'm not sure I'd want to necessarily block the warning message, as people sometimes get upset when we restrict the dependencies of our libraries more heavily than we need to (at least on the node client library -- I have less familiarity with python dependency management), but I think at the very least we should update requirements.txt so people can't use this with urllib3 v2.1.0 (whenever that comes out), and I've submitted a PR for that in our upstream repo.

[phoenixy1]

updated requirements.txt as described above