fix: use headers instead of deprecated getheaders() in urllib3 (Python SDK)

[andreagrandi]

In urllib3 the use of getheaders() method is deprecated:

DeprecationWarning: HTTPResponse.getheaders() is deprecated and will be removed in urllib3 v2.1.0. Instead access HTTPResponse.headers directly.

Calls to self.urllib3_response.getheaders() should be replaced with self.urllib3_response.headers to fix this warning.

This pull request fixes the usage of getheaders() by removing the usage of the deprecated method.

Related Issue or Design Document

See the above description for the issue explaination.

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• I have read the contributing guidelines and signed the CLA.
• I confirm that this pull request does not address a security vulnerability.
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[aeneasr]

Unfortunately, these are auto-generated files and these changes won't have an effect