Get off of pip 20.0.0

pypa/pip#7626

.github/workflows/rust.yml

@@ -34,6 +34,7 @@ jobs:
  - name: py-install
  run: |
  pip install -r ctoybox/requirements.txt
+ pip install --upgrade pip
  pip install maturin
  - name: build-wheel
  working-directory: ./ctoybox