fix(http-client-python): prevent external entity parsing

[joekiller]

Problem:
The python http client uses xml.etree.ElementTree which can open the client up to XML external entity injection (XXE).

Issue:
#8083

Solution:
Explicitly use element tree parser with resolve_entities set to False.

References:

• Snyk XML external entity injection (XXE) / Python

[joekiller]

@microsoft-github-policy-service agree

[github-actions]

All changed packages have been documented.

• ✅ @typespec/http-client-python

Show changes

@typespec/http-client-python - fix ✏️

Explicitly use element tree parser with resolve_entities set to False

[iscai-msft]

@joekiller thank you for the pr! we don't want to add a third-party xml library that all generated libraries will have to depend on. I'm going to keep playing with your first attempt with the native xml library, and see if I can get things passing. Thanks!