Assess impact of bpo-22708 in our library and test suite.

[jalopezsilva]

See https://github.com/python/cpython/pull/8305 for context.

The HTTP CONNECT message will be upgraded to HTTP/1.1 from HTTP/1.0. I expect a small set of changes in the library itself.

[graingert]

This got merged 2 weeks ago

[pquentin]

Yes, but it barely missed 3.12.0 alpha7 that we're using now through GitHub Actions. The commit will be in 3.12.0 beta1 next month, at which point we will start seeing failures.

It would be nice to fix them before that, of course. But it would require someone to compile Python 3.12 and run our test suite first.

[graingert]

I backported the def _tunnel(self): method from 3.12 and ran the tests on 3.11 and everything passed still, so I don't think any changes are needed from urllib3 for this.