ci: bump pytype to 2022.03.29 This is as far as we can go without running into issues with the vendored `attr` package. I tried updating that to the latest, and not only did it not fix the issue, but test-util.py failed due to some poking at `attr` internals that apparently is no longer valid. The `libcst` package is now pinned to what I have locally because trying to install the latest (0.4.7) complains that it can't find the Rust compiler. We should probably use a requirements file instead (and/or figure out why it can't find the Rust compiler), but I don't feel like dealing with another side quest.