* Restores CI to a green state to aid in landing other changes.
* Python 2.7 is still covered, but only on Ubuntu and excluding PyPy. Changes are made to `requirements.txt` et al to ensure this works.
* Runner versions are pinned to avoid automatic breakage, required statuses are updated to match. 
* Codecov action is updated, token is now explicitly passed. 
* Fixes an integration test breaking due to backend changes, to be investigated separately.

The SDK no longer provides a CA bundle to verify SSL connections. This also allows us to remove the runtime dependency on `pkg_resources` and thus `setuptools`. 

The `ca_certs` parameter is still supported, so users can pin with their own CA bundle if they so choose. Otherwise, the default verification mechanism in the `requests` library now applies (this uses `certifi` and/or system certificates, depending on the configuration).

Improves integration tests to cover both scenarios (i.e. when a bundle is provided, and when one isn't).

Manual Spec Update
c8364404953d875801d496a81f786c5545f78223

…#500)

* Per the [docs](https://blog.readthedocs.com/migrate-configuration-v2/), ReadTheDocs now requires a `version 2` config file. In it, we pin the version used to generate the docs to Python 3.7, which matches what is currently tested (and green) in CI.
* PyPI uploads were still configured to run on the latest version of Python (currently 3.12). We pin this back to Python 3.7, which make it less likely to break in mysterious ways.

Reverts the version requirement for requests to what it was prior to dropbox#492.