Note that we don't have to worry about this on develop/non-backport branch, because for later versions of python we just grab the prebuilt cryptography wheel (don't have to build it ourselves) but I guess this isn't available for old versions of python.
Before this PR
CI fails at publish step - e.g. https://app.circleci.com/pipelines/github/palantir/conjure-python-client/234/workflows/f3350813-a430-4a0a-aff0-2ea4b1c7d950/jobs/3035
This is because we're building the cryptography wheel, which requires a rust toolchain to exist. See https://cryptography.io/en/3.4.2/installation.html#rust
Note that we don't have to worry about this on develop/non-backport branch, because for later versions of python we just grab the prebuilt cryptography wheel (don't have to build it ourselves) but I guess this isn't available for old versions of python.
https://app.circleci.com/pipelines/github/palantir/conjure-python-client/225/workflows/73d78499-c600-4f09-a66e-f5ee01a1c47f/jobs/2990
After this PR
==COMMIT_MSG== Install a rust toolchain to fix the publish step ==COMMIT_MSG==
Example successful build step https://app.circleci.com/pipelines/github/palantir/conjure-python-client/241/workflows/a27fffef-85c5-465c-a071-9b253199d90c/jobs/3062
Possible downsides?
Costs 15 seconds to install...